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Re: [SLUG] recovering xfs


jam <jam@xxxxxxxxx> writes:
> On Friday 15 May 2009 21:03:06 slug-request@xxxxxxxxxxx wrote:
>> > Lessons learnt:
>> >
>> > - a journalling file system is bigger than what you see,  3Tb is
>> >   really 3.3Tb when doing a direct copy.
>> >
>> > - Get lots of harddisk in the beginning.   750G drives really only
>> >   give you 698G.  It is annoying to be 300G short and have to go to
>> >   the shop again.
>> >
>> > - Expect lots of wait time,   hard errors on raid take a long time
>> >   to give up.
>> >
>> > - Don't promise anything, expect it to fail.
>> >
>> > - LVM is really cool and well worth the time to rad up on it.   I
>> >   am now going to LVM my home system.
>>
>> I'm planning to do this as well.
>>
>> I was thinking back to Mary's backup post last year and thinking if I
>> could do lvm snapshots with an external harddrive.

LVM snapshots are useful for getting a consistent backup, but just
copying the bits is necessary for a real one.  You might snapshot, then
use the snapshot as the source of your backup if you run a database
server or something similar though...

>>  Still a bit new to lvm though. I think you have to install the
>> alternate ubuntu cd to get lvm right? (unless you are using the
>> server install instead of the desktop).

IIRC you can get LVM, but not software RAID, from the Ubuntu graphical
installer.  The alternate installer can do all of the above.

> Terry Pratchett says the chance of a million to one event happening is 9/10.

...which is great for comedic effect, but not actually an expression of
real statistics.

Well, and a comment on the pretty awful ability of humans to accurately
assess and rate risk.


> LVM is really kewl iff you do frequent (daily) backups.  Otherwise we
> await your plainted cry about how you lost 100 zigabytes of unique
> photos ...

So, can you actually support your claim that LVM is disastrously
unreliable with some, you know, evidence?

I am curious to know, you see, because I have tens of terabytes of data
sitting on LVM[1] across a wide range of machines, scaling from
single-disk workstations through software-RAID servers to serious
bulk-storage systems with hardware RAID.

We have ... well.  It probably suffices to say that we would notice
fairly quickly if LVM was, in fact, unreliable.

Regards,
        Daniel

Besides, no one here is stupid enough to have their systems running
*without* a daily backup, and without routinely checking it, right?

Footnotes: 
[1]  ...and XFS, to introduce the other technology that people love to
     make grandiose claims about the data-destroying abilities of.