Haudy Kazemi wrote:
Hello,
I've looked around Google and the zfs-discuss archives but have not
been able to find a good answer to this question (and the related
questions that follow it):
How well does ZFS handle unexpected power failures? (e.g.
environmental power failures, power supply dying, etc.)
Does it consistently gracefully recover?
Mostly. Unless you are unlucky. Backups are your friend in *any*
environment though.
Should having a UPS be considered a (strong) recommendation or a
"don't even think about running without it" item?
There has been quite any interesting thread on this over the last few
months. I won't repeat my comments, but it is there in digital posterity
on the zfs-discuss archives.
Certainly in a large environment with a lot of data being written, then
one should consider this a mandatory requirement if you care about your
data. Particularly if there are many links in your storage chain that
cause data corruption due to power failure.
Are there any communications/interfacing caveats to be aware of when
choosing the UPS?
In this particular case, we're talking about a home file server
running OpenSolaris 2009.06.
As far as a home server goes, particularly if it is not write intensive
then you will 'most likely' be fine. I have a home one with a v120
running S10 u6 with a D1000
and 7 x 300 GB SCSI disk in a RAIDZ2 that has seen numerous power
interruptions with no faults. This machine is a Samba server for my Macs
and printing
business.
I also have another mail / web server also on another v120 which
experiences the same power faults and regularly bounces back without
issues. But your mileage may vary. It all really
depends on how much you care about the data really.
I haven't used OpenSolaris specifically however as I prefer the
generally more well supported S10 releases. (yes I know you can get
support for OS, but I tend to be
conservative and standardize as much as possible. I do have millions of
files stored on ZFS volumes for our Uni and I sleep well ;))
Actual environment power failures are generally < 1 per year. I know
there are a few blog articles about this type of application, but I
don't recall seeing any (or any detailed) discussion about power
failures and UPSes as they relate to ZFS. I did see that the ZFS Evil
Tuning Guide says cache flushes are done every 5 seconds.
The flush time you mention is based on older versions of ZFS, newer ones
can have a flush time as long as 30 seconds I believe now.
Here is one post that didn't get any replies about a year ago after
someone had a power failure, then UPS battery failure while copying
data to a ZFS pool:
http://lists.macosforge.org/pipermail/zfs-discuss/2008-July/000670.html
Both theoretical answers and real life experiences would be
appreciated as the former tells me where ZFS is needed while the later
tells me where it has been or is now.
Thanks,
-hk
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