Backing up Time Machine restores

On Mar 21, 2008, at 6:50 AM, Bill Rowe wrote:
> On 3/20/08 at 6:42 AM, acetidbits.com (Adam C. Engst) wrote:
>
>> As a new backup needs space, Time Machine is supposed to prune the
>> oldest backups to make space, right?
>
> This is exactly what should be happening and what I see. I've
> been running Time Machine from the first day I installed Leopard
> with the default settings. Currently, when I use the Time
> Machine interface, I see hourly backups for today and yesterday,
> daily backups before yesterday to 2/20/08 and weekly backups for
> dates earlier than 2/20/08.

That is a different process, which happens regardless of fullness or
non-fullness of the TM volume. On the machine I'm typing on now, the
TM volume has 116G available out of 166G. And the oldest backup is
dated Oct 28, 2006, with that same pattern. Backed up volume is 80G
usually having around 30G available.

The pruning for fullness will eventually take away the Oct 28, 2006
backup (and the files that were only in that one, and as many later
backups as need to make room). Unless I decide to use some free space
on the drive, which I carefully arranged to be next above the TM
volume in case I want use it to expand the TM volume. (Then there is
a volume for one of my SuperDuper clones--the other is much more
sensibly on a different spindle.)

   --John

On Mar 21, 2008, at 6:48 AM, Alexander Hoffman wrote:
> That's my understanding, too. However, TM is claiming that there is
> not enough room to do a backup, there only being 30GB and it needs
> 140GB.
>
> So, in some cases at least, it is unable to prune old backups to make
> room for new backups.

A friend experienced a similar problem. For some reason, Time Machine
decided it needed to back up her entire system again. Unfortunately, a
single full backup used more than half of the disk, so Time Machine
couldn't fit the second copy on there. It then proceeded, without
warning, to delete every incremental backup except the last one in an
attempt to free up space. Obviously, it failed to do so. It only
succeeded in deleting all her backups for the past few months.

So Time Machine has at least two major problems: First, why did it
suddenly decide to back up her entire system again? The log files
showed the previous incremental backup completed with no errors.
Second, when Time Machine runs out of space, it does not delete
backups intelligently. It should know if deleting will free up enough
space, and if it won't, it shouldn't delete the old backups.

I've noticed in most "Is Time Machine right for you?" articles is the
assumption that Time Machine works as advertised, despite the fact
that it's a new technology. My experience has been that while it works
most of the time, there are still significant problems, and these
problems should be a factor in answering that question.

--On March 21, 2008 6:50:54 AM -0700 Bill Rowe <readlistssbcglobal.net>
wrote:

> On 3/20/08 at 6:42 AM, acetidbits.com (Adam C. Engst) wrote:
>
>> As a new backup needs space, Time Machine is supposed to prune the
>> oldest backups to make space, right?
>
> This is exactly what should be happening and what I see. I've
> been running Time Machine from the first day I installed Leopard
> with the default settings. Currently, when I use the Time
> Machine interface, I see hourly backups for today and yesterday,
> daily backups before yesterday to 2/20/08 and weekly backups for
> dates earlier than 2/20/08.

This is one of things I don't like about Time Machine. It starts pruning
based on date even if there is a ton of space. It only keeps hourly backups
for 2 days. Then it keeps daily backups for around 30 days. Then it keeps
weekly backups until you run out of space.

On my drive I could probably keep daily backups back to Jan 19th, the day I
started using Time Machine, and still not be close to having a full drive.

Kevin

On Fri, 21 Mar 2008, LewisGmail wrote:

> On 16-Mar-2008, at 11:18, Kevin van Haaren wrote:
> > If your TM disk can't hold at least 2 full copies of your data it's
> > too small.
>
> No, this is completely a function of how much your data changes. For
> example, my in-laws would be perfectly served with a TM backup that
> was 100GB for their 80GB drive (of which about 65GB is used). 100GB
> would be enough to backup their entire system, and keep incrementals
> for at least a year.

It would be nice if there were published guidelines for this.

The official advice had been "the TM drive has to be at least as big as
the boot drive", but there's clearly more to it than that.

When I tried to set up TM to back up the 500gb boot drive on my PMG5 to
a new external 500gb drive, it wouldn't start at all. The drive is
around 80% full (so 400gb used, give or take), but TM claimed that the
backup drive had to be at least 600gb to do a first backup.

Clearly there's some kind of overhead, but 200gb of it? Criminy. Yes, I
could have gone for a bigger external drive, but without some kind of
guidelines as to how much bigger it really needs to be, it seems like a
fool's errand to force it to work. The backup history is nice, but all I
really *need* is a mirror drive, and if TM won't even do that, then the
fancy GUI doesn't really amount to much for me.

So I gave up & went back to using rsync, as I did under Tiger. It isn't
as fancy, but it has the significant advantage of actually working.


--
Chris Devers

--On March 21, 2008 6:48:57 AM -0700 "LewisGmail" <gkremegmail.com> wrote:

> On 16-Mar-2008, at 11:18, Kevin van Haaren wrote:
>> If your TM disk can't hold at least 2 full copies of your data it's
>> too
>> small.
>
> No, this is completely a function of how much your data changes. For
> example, my in-laws would be perfectly served with a TM backup that
> was 100GB for their 80GB drive (of which about 65GB is used). 100GB
> would be enough to backup their entire system, and keep incrementals
> for at least a year.

Rules of thumbs always have assumptions behind them and exceptions to them.
However in this case, I'd say the difference between 100GB and 130GB is
negligable and that they did size their TM drive to be at least 2x data.

And yes if you want to spend an hour trying to figure out how fast your
data changes and try to pinpoint an exact drive size go ahead, but as a
rule of thumb I would start out with 2x your data and size up for the
longer you want to be able to store data (my drive is 5x data size). This
assumes a full backup can be made and if every single file on your drive
changes you'll get 2 backups of your files.

Also if you're trying to make as small a TM drive as possible (again
something I don't suggest) remember that every security update, major
update, application update, causes file changes on your system. For
example, yesterday I applied 7 updates from Apple totalling a download of
149MB. My TM backup after the install grew by 1GB. If I remember
correctly, going from 10.5.1 to 10.5.2 was 4 or 5 gb of file changes in TM.

At 4:22 PM -0700 3/21/08, Chris Devers wrote:
>So I gave up & went back to using rsync, as I did under Tiger. It isn't
>as fancy, but it has the significant advantage of actually working.

I think that Chris overstates the case.

I think that Time Machine DOES work, and works quite well. It is
largely idiot proof, runs automatically and it makes it very easy to
do restores.

Yes, there are a couple of glitches, but they won't be hit by most
user, not by many at all.

Every backup system is going to have issues when the backup media is
full. What do you want to happen at that time?

Should it just stop functioning? In some circumstances, that would be
a good idea. (i.e. you don't want to lose any old backups.)

Should it delete the oldest backups? In some circumstances that would
be a good idea. (i.e. you want to be able to recover recent data, but
are less likely to worry about the oldest data.)

Should it delete recent but not the MOST recent backups? In some
circumstances that would be a good idea. (It gets complicated,
depending on exactly what the strategy is.)

I don't agree with all of TM's design decisions, but I don't think
that it just doesn't work.

rsync is fine - as are any number of other synchronization tools -
but they serve a different purpose, or at least a more limited
purpose than TimeMachine.
--
=Alex Hoffman
Leadership, Policy & Politics
Teachers College, Columbia University

--On March 21, 2008 4:22:47 PM -0700 Chris Devers <cdeverspobox.com> wrote:

> It would be nice if there were published guidelines for this.
>
> The official advice had been "the TM drive has to be at least as big as
> the boot drive", but there's clearly more to it than that.

The very first backup TM makes is a complete backup of your hard drive,
skipping the folders specified in the settings. If you backup drive is as
large as your boot drive, you'll get one copy of your boot drive and that's
it. That advice is the absolute minimum drive size.

> The backup history is nice, but all I
> really *need* is a mirror drive, and if TM won't even do that, then the
> fancy GUI doesn't really amount to much for me.

The fancy GUI doesn't do anything for a mirror situtation. The GUI shows
you files as they have changed over time. With a mirror there is only ever
one file.

> So I gave up & went back to using rsync, as I did under Tiger. It isn't
> as fancy, but it has the significant advantage of actually working.

TM's benefit is the multiple backups over time. However this is pretty
worthless for files that don't change over time (i.e. music/movie files in
iTunes). For those files a simple mirror really is best. What I would do
in your situation is use both TM and rsync. Identify which files you
actually want mulitple copies of and which files you just want a mirror of.
For example, I backup everything except my iTunes library (which is 270GB)
but my Documents folder is the key folder. It has my files that change the
most frequently and are most likely the files I need back multiple versions
ago.

If you trim out folders of files that are rarely changing and just use
rsync for those, and TM for other folders, you'll have the best of both
worlds.

Kevin

The major appeal of Time Machine is this: connect an external hard
drive, assign it to Time Machine, and be done with it.

Compared to any other versioning backup software, this is the easiest-
to-setup and easiest-to-use option out there. It's so simple, even
total computer rookies should get it. So, why add any complexity if
this does not provide any real benefit to the average user?


Lewis Butler wrote:

>> If your TM disk can't hold at least 2 full copies of your data it's
>> too small.
>
>
> No, this is completely a function of how much your data changes.

For the vast majority of users, the rule of thumb that the backup
drive should be about twice the size of the drive(s) that will be
backed up to it, will work out just fine. With brand-name external
drives selling at prices around 110€ for 160 gigs or 130€ for 200, I
don't think that investing any time into analyzing a user's behavior
to optimize the backup drive's size is worth it.

(Unless you're an audio or video pro, in which case twice-the-size
probably won't do.)


kevinv wrote:

> It only keeps hourly backups for 2 days. Then it keeps daily backups
> for around 30 days. Then it keeps weekly backups until you run out
> of space.
>
> On my drive I could probably keep daily backups back to Jan 19th,
> the day I started using Time Machine, and still not be close to
> having a full drive.

Again, think simplicity: "one day of hourly backups, one month of
daily backups, weekly backups until the drive is full" is easy to
understand for any user. Why make it more complex?

If Time Machine would employ a more complicated algorithm, what should
that look like: why just keep daily backups for a few weeks (and for
how _many_ weeks)? What about hourly: space permitting, keep them for
a week? Two weeks? A month? Imagine what the Time Machine UI would
look like if you kept some 168 hourly backups per week (assuming that
the machine won't go to sleep, of course ;) ), instead of (eventually)
just one.


cdevers wrote:

> It would be nice if there were published guidelines for this.

>

> The official advice had been "the TM drive has to be at least as big
> as the boot drive", but there's clearly more to it than that.

That comment proves my point, I think, that the way Time Machine works
should be kept as simple as it is right now. Because: there _is_ a
guideline, and, no, there is _not_ more to it.

As outlined earlier, the guideline for buying backup hard drives that
will work for the average user, is this: make it about twice as big as
the combined size of all the drives (not just the boot drive) you want
to back up to it. That way, you don't have to worry about running out
of space, even if you use all your hard drives to their full capacity
and even when a lot of data does change regularly.


> The backup history is nice, but all I really *need* is a mirror
> drive, and if TM won't even do that, then the fancy GUI doesn't
> really amount to much for me.

Why not combine them: e.g., SuperDuper! can use the Time Machine
volume (not just the same drive!) as its own target drive, so you can
have both a versioned Time Machine backup _and_ a bootable mirror on
the same volume. Best of both worlds. (Don't forget to throw an off-
site backup into the mix, as well!)

<shirtpocket.com/SuperDuper>


If, however, you still feel that Time Machine won't cut it for you,
there are plenty of other backup solutions available for the Mac. For
most users that might never have backed up until Leopard came along,
TM is fine just as it is. No need to mess with it at all, methinks


Regards,

Jochen.

--On March 21, 2008 6:48:57 AM -0700 Dave Scocca <davescocca.org> wrote:

>
> What this means, in a practical sense--given that Time Machine will over
> time
> generally keep its backup disk full--is:

Yes, but remember it also does time based pruning if the drive is full or
not. It keeps hourly backups for 2 days, then prunes back the hourlys to
the first one taken that day. It keeps these daily snapshots for 30 days,
then prunes back to one backup per week. The weekly backups are then kept
until the drive is full.

If you delete a file on Tuesday and your weekly backups are from Sunday,
you may lose the file anyway after 30 days no matter what size disk you
have.

On 03/21/2008 18:22 PM, "Chris Devers" <cdeverspobox.com> wrote:

> When I tried to set up TM to back up the 500gb boot drive on my PMG5 to
> a new external 500gb drive, it wouldn't start at all. The drive is
> around 80% full (so 400gb used, give or take), but TM claimed that the
> backup drive had to be at least 600gb to do a first backup.

Because backups always have overhead beyond the files they back up. Backup,
especially incremental != File Copy.

>
> Clearly there's some kind of overhead, but 200gb of it? Criminy. Yes, I
> could have gone for a bigger external drive, but without some kind of
> guidelines as to how much bigger it really needs to be, it seems like a
> fool's errand to force it to work.

Because there's no way to do that, usage conditions are too different. The
extra 200GB would give you enough space for overhead and a decent sized
history. Maybe. Unless you want to have TM force you to answer a long
questionnaire about what you do with your computer, how is it supposed to
estimate space?

> The backup history is nice, but all I
> really *need* is a mirror drive, and if TM won't even do that, then the
> fancy GUI doesn't really amount to much for me.

RAID != Backup. RAID is designed for reliability, not archiving. Mirrors
don't keep a history, and any change you make, for good or ill, propagates
instantly. RAID != Backup

>
> So I gave up & went back to using rsync, as I did under Tiger. It isn't
> as fancy, but it has the significant advantage of actually working.

I'd hardly say that rsync under Mac OS X 10.4 worked, considering all the
problems it had.

--
John C. Welch

On Mar 23, 2008, at 4:13 AM, Kevin van Haaren wrote:
> And yes if you want to spend an hour trying to figure out how fast
> your
> data changes and try to pinpoint an exact drive size go ahead, but
> as a
> rule of thumb I would start out with 2x your data and size up for the
> longer you want to be able to store data (my drive is 5x data size).
> This
> assumes a full backup can be made and if every single file on your
> drive
> changes you'll get 2 backups of your files.

What I did to size my TM volumes was to look at the disks already
attached to the two Leopard machines, leave room for other stuff, and
make a guess. And I left unused space after the TM volume in both
cases, which can be used for something else or for expanding the TM
volume.

In one case, that guess was "this partition at the start of the drive
looks big enough". Later I realized that I didn't need two SuperDuper
clones on that drive, and changed the one adjacent to the TM volume to
unused space. (I also keep a SuperDuper clone on another drive.)

In the other case, I started out using the largest partition on the
drive. Then I learned what Disk Utility can and cannot do, and redid
the disk with a partition at the start of the drive slightly larger
than that had been, followed by unused space. (That meant tossing
out two days of Time Machine backups for what is essentially a sandbox
machine, and starting over.)

So you can see that my TM volume sizing was carefully calculated.

   --John

On Mar 23, 2008, at 4:13 AM, Alexander Hoffman wrote:
> rsync is fine - as are any number of other synchronization tools -
> but they serve a different purpose, or at least a more limited
> purpose than TimeMachine.


One thing that rsync does not do and has no hope of doing is to induce
the 95% (pick your own number) of Mac users who don't back up to start
doing so. TimeMachine has induced some of that group to back up.

   --John

On Mar 24, 2008, at 7:16 AM, John C. Welch wrote:
> On 03/21/2008 18:22 PM, "Chris Devers" <cdeverspobox.com> wrote:
>
>> Clearly there's some kind of overhead, but 200gb of it? Criminy.
>> Yes, I
>> could have gone for a bigger external drive, but without some kind of
>> guidelines as to how much bigger it really needs to be, it seems
>> like a
>> fool's errand to force it to work.
>
> Because there's no way to do that, usage conditions are too
> different. The
> extra 200GB would give you enough space for overhead and a decent
> sized
> history. Maybe. Unless you want to have TM force you to answer a long
> questionnaire about what you do with your computer, how is it
> supposed to
> estimate space?

Actually, that's exactly my question -- how *does* it estimate space?
Clearly it got a number from somewhere. Somehow it decided that it
needed 50% more space as overhead. There was no questionnaire
involved, it just jumped to this conclusion.

My thinking is that in the degenerate case, TM should, given backup
space at least equal to that of the source data, be able to create at
least one full copy of that source. If you give it more, that's better
of course, but if all else fails it should at least be able to make
one backup copy. In my case, it refuses to do that.

>> The backup history is nice, but all I
>> really *need* is a mirror drive, and if TM won't even do that, then
>> the
>> fancy GUI doesn't really amount to much for me.
>
> RAID != Backup. RAID is designed for reliability, not archiving.
> Mirrors
> don't keep a history, and any change you make, for good or ill,
> propagates
> instantly. RAID != Backup

Groovy. I love when you trot this out. Do you have it bound to a
shortcut in TextExpander or something?

The thing is though, I missed the part where I said anything at all
about RAID.

Oh wait, I remember -- I didn't mention RAID. I just want a second
copy of my data. If and when I do think about adding RAID to the mix
though, I'll surely keep your advice in mind.

>> So I gave up & went back to using rsync, as I did under Tiger. It
>> isn't
>> as fancy, but it has the significant advantage of actually working.
>
> I'd hardly say that rsync under Mac OS X 10.4 worked, considering
> all the
> problems it had.

*shrug*

It has been sufficient for my needs. I just want a spare copy of my
home folder on an external drive so that if the internal drive fails,
or the house catches fire, I can grab the external and go. For me,
rsync is fine for this.

--
Chris Devers

On 03/24/2008 10:48 AM, "Chris Devers" <cdeverspobox.com> wrote:

>>> The backup history is nice, but all I
>>> really *need* is a mirror drive, and if TM won't even do that, then
>>> the
>>> fancy GUI doesn't really amount to much for me.
>>
>> RAID != Backup. RAID is designed for reliability, not archiving.
>> Mirrors
>> don't keep a history, and any change you make, for good or ill,
>> propagates
>> instantly. RAID != Backup
>
> Groovy. I love when you trot this out. Do you have it bound to a
> shortcut in TextExpander or something?

I use TypeIt4Me actually, and no, actually.

>
> The thing is though, I missed the part where I said anything at all
> about RAID.
>
> Oh wait, I remember -- I didn't mention RAID. I just want a second
> copy of my data. If and when I do think about adding RAID to the mix
> though, I'll surely keep your advice in mind.

You said "...but all I really *need* is a mirror drive..." If you don't want
people to see "mirror" and think "oh, RAID 1", then you need to be *far*
more clear on what you mean. I'd bet I could show that sentence to a dozen
sysadmins, and most, if not all of them would take that to mean a well,
mirrored drive. That means, to most people of the right background, a RAID1
set. "mirror" in conjunction with drive has a rather specific meaning. If
you're overloading that to mean "some place where I dump files that I copy
from another drive, so it's not really a mirror, but a storage place" then
you should make that more clear, rather than assuming that everyone knows
you're using a common term outside the norm.

If you say "my car's broken" most people are going to assume automobile, not
train, unless it's the 1870s and your name is James West.

>
>>> So I gave up & went back to using rsync, as I did under Tiger. It
>>> isn't
>>> as fancy, but it has the significant advantage of actually working.
>>
>> I'd hardly say that rsync under Mac OS X 10.4 worked, considering
>> all the
>> problems it had.
>
> *shrug*
>
> It has been sufficient for my needs. I just want a spare copy of my
> home folder on an external drive so that if the internal drive fails,
> or the house catches fire, I can grab the external and go. For me,
> rsync is fine for this.

If you don't mind the problems with metadata and ACLs, then rsync works. But
if you care about both, then it has issues. IIRC, Mac OS X 10.5 fixes these.

--
John C. Welch

At 04:59 on 25-03-2008, John C. Welch wrote:
> then you should make that more clear, rather than assuming that
> everyone knows you're using a common term outside the norm.

Most people are not sysadmins, and your description of the term
mirror drive is certainly not at all what I would call 'common
usage'. You shouldn't assume that everyone views the world as you do.
;-)

_________________
=> Jolin

On Tue, Mar 25, 2008 at 2:15 PM, Jolin M Warren
<JolinWarrenoakandapple.org> wrote:
> At 04:59 on 25-03-2008, John C. Welch wrote:
> > then you should make that more clear, rather than assuming that
> > everyone knows you're using a common term outside the norm.
>
> Most people are not sysadmins, and your description of the term
> mirror drive is certainly not at all what I would call 'common
> usage'. You shouldn't assume that everyone views the world as you do.
> ;-)
>

I'm going to have to side with John on this one. RAID 1 is the
definition of a mirror drive. I definitely side more towards the
technical side, but I can't for the life of me figure out what "mirror
drive" means if it doesn't mean RAID 1. I'm not being snarky here, I
really want to know what mirror drive might mean to the general
computer user.

--
Michael

On 03/25/2008 16:15 PM, "Jolin M Warren" <JolinWarrenOakAndApple.org>
wrote:

>> then you should make that more clear, rather than assuming that
>> everyone knows you're using a common term outside the norm.
>
> Most people are not sysadmins, and your description of the term
> mirror drive is certainly not at all what I would call 'common
> usage'. You shouldn't assume that everyone views the world as you do.
> ;-)

I don't. But I *am* a sysadmin, a fact Chris is *well* aware of. He's also
well aware of the common (within the computer industry) meaning of the term
"mirror" as it extends to drives. The fact that I pointed out mirroring
doesn't equal backup should be of no surprise to him, because it's an
accurate statement. Should I assume random meanings for terms, and hope I
guess correctly?

The "oh, I have a mirror, I don't need to back up" meme is a common one, and
one I have seen cause people problems. If you have a mirror, and you get a
corrupt file, you know what you have?

Two corrupt files.

Not a backup, but two corrupt files. So much for "mirror = backup".

As well, when you talk to someone about a problem, which is it better to be,
more, or less clear.

Do you tell your doctor, "I'm sick, make me better" and seriously expect a
correct diagnosis based solely on your statement? No.

If you tell your doctor over the phone, "I have a headache" but in fact, you
also have a runny nose and a fever, is it the doctor's fault that they take
you at your words, and tell you to take a couple of tylenol? Hardly.

"attitude" is a common word, yet if you ask a psychologist and an avionics
technician what that word means, you're going to get two rather different
answers. Neither are wrong, but if you expect one to know that you mean the
other's meaning by...some form of telepathy, then you're going to be
disappointed.

This is a text only medium. No one can "know what you mean". You have to
explain it, preferably at length, and in some detail. If you tell someone a,
and you meant b, but you use terminology for a, then they are, regardless of
what you are thinking, going to go with a, unless you provide sufficient
detail for them to realize that you mean b, and you're just using a
incorrectly, at least in that context.

Mirror as applied to has a specific meaning to a sysadmin, just as other
terms have specific meanings in other professions. Don't be surprised that,
when you use a computer term in a computer context in a suboptimal manner,
someone who's a sysadmin points that out.

--
John C. Welch

On Mar 26, 2008, at 8:31 AM, Michael Krzyzek wrote:
> On Tue, Mar 25, 2008 at 2:15 PM, Jolin M Warren
> <JolinWarrenoakandapple.org> wrote:
>> At 04:59 on 25-03-2008, John C. Welch wrote:
>>> then you should make that more clear, rather than assuming that
>>> everyone knows you're using a common term outside the norm.
>>
>> Most people are not sysadmins, and your description of the term
>> mirror drive is certainly not at all what I would call 'common
>> usage'. You shouldn't assume that everyone views the world as you do.
>> ;-)
>
> I'm going to have to side with John on this one. RAID 1 is the
> definition of a mirror drive. I definitely side more towards the
> technical side, but I can't for the life of me figure out what "mirror
> drive" means if it doesn't mean RAID 1. I'm not being snarky here, I
> really want to know what mirror drive might mean to the general
> computer user.

A simple complete duplicate drive, updated either on a schedule
(nightly, weekly, whatever) or whenever I remember to update it,
typically because I just uploaded a bunch of photos or something along
those lines. It wasn't meant to be more or less than that.

It's not all that different from what you'd get if you duplicated the
drive with Disk Utility or Carbon Copy Cloner. Heck, not even that
different from what you'd get if you just dragged things over in the
Finder, except that I want the hidden Unix stuff too (/usr, /
etc, .dotfiles, etc), but it isn't that far off from what I have in
mind. I'm not picky for this kind of thing. Losing metadata & ACLs
isn't a problem for my modest needs.

If I meant RAID, I would have said RAID.

I'm not currently worried about having a history of backups, as I
already have habits to provide me with a history for the files where
I'd want that sort of thing (version control systems, periodic
application-level backup snapshots, etc). I just need a little bit of
redundancy so that if the main drive fails or the house catches fire,
I have a better chance at recovering.

If using "mirror" as a shorthand for "duplicate" threw sysadmins off,
sorry for being imprecise.

  * * * * *

On Mar 26, 2008, at 8:31 AM, John C. Welch wrote:
> On 03/25/2008 16:15 PM, "Jolin M Warren" <JolinWarrenOakAndApple.org>
> wrote:
>> Most people are not sysadmins, and your description of the term
>> mirror drive is certainly not at all what I would call 'common
>> usage'. You shouldn't assume that everyone views the world as you do.
>> ;-)
>
> I don't. But I *am* a sysadmin, a fact Chris is *well* aware of.

:-)

> He's also
> well aware of the common (within the computer industry) meaning of
> the term
> "mirror" as it extends to drives. The fact that I pointed out
> mirroring
> doesn't equal backup should be of no surprise to him, because it's an
> accurate statement.

I realized in hindsight that I was using a "jargon" term in a loose
way. All the same, to me, if I meant RAID, I would have said RAID,
rather than just implying it. The lack of mention of it was, I
suppose, intended to imply that I was speaking more generally.

> This is a text only medium. No one can "know what you mean". You
> have to
> explain it, preferably at length, and in some detail.

*shrug*

I guess the longer I use email, the more I see the benefit of being
succinct. Obviously this thread has spiralled away (and I'm stepping
out of it after this), but in general these days I guess I prefer to
err on the side of being brief (and risking being misunderstood)
rather than being verbose (and spending too much time composing an
email that most people won't have time to read through anyway).

YMMV.

--
Chris Devers

Among the people I work with, "mirrored drive" simply means an exact
clone of another drive. Also implied is that it happens as an
automatic process, so that either writing to one also writes to
another, or alternatively, that the cloning happens at regularly
scheduled intervals. The point being that if one fails you have an
exact copy to back you up, and that it is not subject to you
remembering to do the cloning.

I'm not saying this is perfectly correct as a definition, just that I
know a lot of people who use the term this way.

[And with that, I think we've adequately explored the various definitions of "mirror," so let's not continue it in this thread. -Joe]

Howard

At 01:33 03/27/08 -0700, Chris Devers wrote:
>If using "mirror" as a shorthand for "duplicate" threw sysadmins off,
>sorry for being imprecise.

To those who need TM most, "mirror" refers to a reflector, not to a
reflection. Any use of "mirror" to mean "duplicate" or "reflection" or
"mirror image" is dense jargon, irrespective of which particular bit of
jargon you are using.

When mirrored [sic] disk first came out, I ranted against the odd use of
the word. Obviously I lost that battle, probably lost it even before I even
knew it had started.

Edward
--
Art works by Melynda Reid: http://paleo.org