Mart van Santen wrote:
Hi,
Do the I/O problems go away when only one of the SSDs is attached?
No, the problem stays with only one SSD. The problem is only less when
resilvering, but not totally disappeared (maybe because of the
resilver overhead).
The resilver is likely masking some underlying problem. :-(
Frankly, I'm betting that your SSDs are wearing out. Resilvering
will essentially be one big streaming write, which is optimal for
SSDs (even an SLC-based SSD, as you likely have, performs far better
when writing large amounts of data at once). NFS (and to a lesser
extent iSCSI) is generally a whole lot of random small writes, which
are hard on an SSD (especially MLC-based ones, but even SLC ones).
The resilvering process is likely turning many of the random writes
coming in to the system into a large streaming write to the
/resilvering/ drive.
Hmm, interesting theory. Next I well execute only a resilver to see if
the same happens. I assume when adding a new disk, even though it's
only a slog disk, the whole tank will resilver? If I look to the zpool
iostat currently I see a lot of reads on the separate SATA disks (not
on the tank/or raidz2 pools), assuming resilvering takes place there
and the SSD's are already synced.
I'm not 100% sure, but replacing a device in a mirrored ZIL should only
generate I/O on the other ZIL device, not on the main pool devices.
SSDs are not hard drives. Even high-quality modern ones have
/significantly/ lower USE lifespans than an HD - that is, a
heavily-used SSD will die well before a HD, but a very-lightly used
SSD will likely outlast a HD. And, in the case of SSDs, writes are
far harder on the SSD than reads are.
Is about half a year for these disk not really short? Sure, we have
some I/O, but not that many write operations, about ~80-140 iops,
anyway, I will try to get new disks from SUN (we have SLC disks from
Sun). Is there any knowledge about the life time of SSD's? Maybe in
terms of amount of I/O Operations?
Regards,
Mart van Santen
That's not enough time for that level of IOPS to wear out the SSDs
(which, are likely OEM Intel X25-E). Something else is wrong.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
Timezone: US/Pacific (GMT-0800)
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