ZFS UNMAP performance

[Bob Bishop]

Hi,

On 12 Mar 2014, at 00:28, Danny Schales <dan at 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).

--
Bob Bishop
rb at gid.co.uk