to perform actual powerloss tests, it would be interesting
to hear from anybody whether it is generally expected to be safe.
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about this. Since I wanted to confirm my
understanding of ZFS semantics w.r.t. write caching anyway I thought I might
aswell also ask about the general tendency among drives since, if anywhere,
people here might know.
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/ Peter Schuller, InfiDyne Technologies HB
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with zpool create speedtest c4d0 c5d0 c6d0 c7d0 and
variations of that for the different combinations. The pool with all
four drives is 1.16T in size.
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flushes are handled by zfs.
But it's most definitely faster than the 4 mb/second seen when dd:ing to the
pool.
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for small reads.
Is there some reason why a small read on a raidz2 is not statistically very
likely to require I/O on only one device? Assuming a non-degraded pool of
course.
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actually want it
disabled (the NFS server).
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://opensolaris.org/os/community/zfs/docs/zfsadmin.pdf
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, the statistical
probability of failure is too high for raidz (or raid5). It's a shame the
statement in the guide is not further qualified to actually explain that
there is a concrete issue at play.
(I haven't looked into the archives to find the previously mentioned
discussion.)
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/ Peter Schuller
very relevant for the ZFS administration guide IMO
(and man pages for that matter).
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levels of
redundancy), or alternatively to the unlikely event of bad blocks co-inciding
on multiple drives, wouldn't reliability be significantly increased in cases
where this is an acceptable practice?
Opinions?
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/ Peter Schuller, InfiDyne Technologies HB
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the old data is not
removed.
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.
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http
an
asynchronous method of ensuring relative order of I/O operations to
userland, which is often useful.
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, the above stats are interesting and I suppose consistent
with what one might expect, from previous discussion on this list.
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servers with 5-20 or so terrabytes each, you probably don't need is
all that much - even if it would be nice (speaking from experience).
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type use. Yes
you should avoid it, but shit (always) happens.
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.
But somehow the snapshot situation feels a lot more risky.
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something along the lines of:
zfs destroy snapshot:/path/to/[EMAIL PROTECTED]
Where the use of snapshot: would guarantee that non-snapshots are not
affected.
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snapshots or clones.
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Apparently (and I'm not sure where this is documented), you can 'rmdir'
a snapshot to remove it (in some cases).
Ok. That would be useful, though I also don't like that it breaks
standard rmdir semantics.
In any case it does not work in my case - but that was on FreeBSD.
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for privilege delegation.
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the zfs
command is documented to guarantee backward compatible output?), but in
cases like this it really really becomes critical.
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requirement.)
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/raidz2 array that you then stripe between.
I believe zpool should have warned you about trying to add a
non-redundant component alongside the redundant raidz, requiring you to
force (-f) the addition.
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observations
if it actually did flush caches.
The ability to get decent performance *AND* reliability on cheap disks
is one of the major reasons why I love ZFS :)
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problems on both Solaris and FreeBSD (with AFAIK independent USB
implementations), but work in Windows...
If you have luck with that then please post some public info as I am sure I
would not be the only one to be interested in it. Wonder what those 8-ways
cost new...
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/ Peter Schuller
of this information).
AFAIK the ZFS pools themselves are fully portable.
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Now, what if that system had been using ZFS root? I have a
hardware failure, I replace the raid card, the devid of the boot
device changes.
I am not sure on Solaris, but on FreeBSD I always use glabel:ed
devices in my ZFS pools, making them entirely location independent.
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/ Peter Schuller
data? I am not read up on the details of the ARC. But in this
particular case it was clear that a simple LRU had been much more
useful - unless there was some other problem related to my setup or
FreeBSD integration that somehow broke proper caching.
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...
If I get anything confirmed from LSI I'll post an update.
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advocated to me.
Seriously.)
[2] Because of [1] and because of course you only run stable software that is
well tested and will never be buggy. (This has been advocated. Seriously.)
[3] Because of [1].
[4] Because of [1], [2] and [3].
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a show stopper unless you
can throw money at the problem.
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and da6.
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before
resuming writes.
Note that this is also being run on plain hardware; it's not even PCI Express.
During throughput peaks, but not constantly, the bottleneck is probably the
PCI bus.
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a poke at the
streaming performance. Very interesting to hear there's a bug open for it
though.
Can you also post iostat -xnz 1 while you're doing dd?
and zpool status
This was FreeBSD, but I can provide iostat -x if you still want it for some
reason.
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/ Peter Schuller
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I was just wandering that maybe there's a problem with just one
disk...
No, this is something I have observed on at least four different systems, with
vastly varying hardware. Probably just the effects of the known problem.
Thanks,
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must expose the individual disks to your mirror/raidz/raidz2 individually
through the virtualization environment and use them in your pool.
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.
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here and on FreeBSD lists about not seeing
the added space. In my case I always rebooted anyway so I could never tell
the difference.
I stand corrected. Thanks!
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believe for the 5-bay
supermicro; the Lian Li stuff is cheaper, but not hotswap and such).
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it. You can choose your desired level of redundancy expressed
as a percentage of the file size.
[1] http://en.wikipedia.org/wiki/Parchive
[2] http://en.wikipedia.org/wiki/Forward_error_correction
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, I was unable to completely disable write caching either because
that, too, did not actually propagate to the underlying device when
attempted.
(I could not say for certain whether this was fundamental to the
device or in combination with a FreeBSD issue.)
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.
speculation
I think it boils down to the fact that 99% of customers that aren't
doing integration of the individual components in overall packages,
probably don't care/understand/bother with it, so as long as the
benchmarks say it's fast, they sell.
/speculation
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of weeks later.
While I don't know what is going on in your case, blaming the
introduction of a piece of software/hardware/procedure on some problem
without identifying a causal relationship, is a common mistake to
make.
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/ Peter Schuller
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problems
arrising from misbehaving hardware or bugs in software. ZFS cannot
magically overcome such problems, nor can UFS/reiserfs/xfs/whatever
else.
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device was ignoring sync
commands. But I have no idea what the case was for the original
poster, nor have I even followed the thread in detail enough to know
if that would even be a possible explanation for his problems.
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of a non-enterprisy case where you do care
about persistence, is the pretty common case of simply running a mail
server. Just for anyone reading the above paragraph and concluding it
doesn't matter to mere mortals ;)
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, not using a
hardware raid volume.)
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faster on ZFS... but this won't happen until operating systems start
exposing the necessary interface.
What does one need to do to get something happening here? Other than
whine on mailing lists...
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issues started being seriously discussed in the
Linux kernel community for example).
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confirm/deny? If the
latter, is there some way to tweak it? I have not found one (other
than changing the code). Is there any particular reason why such knobs
are not exposed? Am I missing something?
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* to be
a pure LRU by design. Again, there may very well be a FreeBSD specific
issue here that is altering the behavior, and maybe the extremity of
it that I am reporting is not supposed to be happening, but I believe
the issue is more involved than what you're implying in your response.
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/ Peter
want the cache to behave in a
way where I do not need gigabytes of extra ARC size to lure it into
caching the data necessary for 'urxvt' without having to start it 50
times in a row to accumulate statistics.
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a bigger cache
size in relation to the working set in order to be effective in the
way I am using it here. I was basing my expectations on LRU-style
behavior.
Thanks!
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.
(I realize I should investigate properly and report back, but I'm not
likely to have time to dig into this now.)
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, they have to be removed.
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