Date: Wed, 12 Mar 2014 10:07:02 -0500 From: Eric van Gyzen <eric@vangyzen.net> To: Bob Bishop <rb@gid.co.uk>, Danny Schales <dan@LaTech.edu> Cc: freebsd-stable@freebsd.org Subject: Re: ZFS UNMAP performance Message-ID: <53207816.7030104@vangyzen.net> In-Reply-To: <C7680FD4-885B-4295-9D82-AB1CF869B928@gid.co.uk> References: <531F2BA0.6000105@LaTech.edu> <CAFHbX1JghVaQ3xM2OZ6jpWOs6tn=Z8epd8Om3NW_CDnZHPSdng@mail.gmail.com> <531F3503.8090403@LaTech.edu> <531F767C.3040105@LaTech.edu> <531F8EAA.1020107@vangyzen.net> <531FAA20.7080407@latech.edu> <C7680FD4-885B-4295-9D82-AB1CF869B928@gid.co.uk>
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On 03/12/2014 05:01, Bob Bishop wrote: > Hi, > > On 12 Mar 2014, at 00:28, Danny Schales <dan@LaTech.edu> wrote: > >> On 3/11/2014 5:31 PM, Eric van Gyzen wrote: >>>> Replying to myself...I note that the system is reporting that TRIM is >>>> being used. Is this normal for non-SSD systems? There *is* SSD in the >>>> system, but I'm pretty sure the system can't tell it's SSD (it's hidden >>>> behind a Dell PERC card). The number of trim.successes is roughly >>>> equivalent to the number of deletes reported by gstat for the ISCSI LUN >>>> devices. Should the system be using TRIM for ISCSI LUNs? >>> Sure, if the LUN (i.e. the storage controller) reports that it supports >>> TRIM/UNMAP. Note that this is completely unrelated to the type of disks >>> that provide the LUN's backing store. >>> >>>> kstat.zfs.misc.zio_trim.bytes: 232845656064 >>>> kstat.zfs.misc.zio_trim.success: 30810983 >>>> kstat.zfs.misc.zio_trim.unsupported: 809 >>>> kstat.zfs.misc.zio_trim.failed: 0 >>>> >>>> Danny >>>> >> Are there any risks to turning off TRIM to see if the performance >> improves (other than the loss of space recovery)? >> >> Danny > If the backing store really is SSD then turning off TRIM should hurt write performance eventually (and read to a lesser extent). Correct. If it's not SSD, though, the loss of space recovery should be the only risk. And I imagine your highest tier of storage is not SSD. Eric
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