On 8/7/16 8:07 PM, Garrett D'Amore wrote:
> historically some ssds have performed worse with trim as they do
> some expensive operations. i have not looked at the webrev yet
> but are there tunables or an administrative interface to this?
By default, everything is off, so there are no performance
implementations "out of the box". The administrative interfaces are, either:
* enabling automatic trimming after deleting data:
# zpool set autotrim=on <poolname>
* manually initiating a single full-pool trim (running through
all the free space on a pool and trimming it):
# zpool trim <poolname>
Automatic trim is as the name implies: fully automatic. You just delete
data and ZFS will at some later point, if the blocks have not been
reused, simply trim those blocks out.
Manual trim behaves much like a scrub. It has an adjustable rate (in
bytes/sec) and can be monitored through "zpool status" or stopped at any
time via "zpool trim -s <poolname>".
> how diverse in terms of ssds has this been tested with?
We've tested primarily with Sandisk SAS SSDs, mainly the Optimus line
and on some pretty high-end kit (Sandisk's INFINIFLASH).
> are there performance implications observed?
Yes, this is detailed in the manpage. In general, Optimus 1 takes poorly
to automatic trim and can suffer a write throughput limitation when lots
of deletes are going on. On Optimus 2 and the IF100 the performance
impact was much smaller (measurable, but really not much).
In general, the manpage suggests a "test and see what works" approach.
Try autotrim=on and see if it affects performance on your system. If it
doesn't, leave autotrim on. If it does, disable autotrim and use manual
trim during a maintenance window to still get most of the used block
recovery benefits.
Cheers,
--
Saso
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