[linux-lvm] Questions about issue_discards
snitzer at redhat.com
Fri Dec 7 14:18:27 UTC 2012
On Thu, Dec 06 2012 at 5:25pm -0500,
CJ Kucera <pez at apocalyptech.com> wrote:
> Hello, list!
> I've started to play around with SSD drives and was curious about a
> couple aspects of the issue_discards configuration option.
> 1) The lvm.conf comments note that when enabled, it'll still only
> (obviously) issue discards to storage which happens to support it. Is
> there a way of querying block devices to find out if they support the
lvm will only issue discards if the underlying device has non-zero
discard_granularity and discard_max_bytes, to check:
(replace <dev> accordingly, e.g. sda)
> 2) Would a change to the issue_discards parameter be picked up
> automatically by the running kernel? The lvm.conf manpage mentions that
> it remembers the timestamp of the file "between commands" and will apply
> changes then, but it almost sounds like that'd be mostly for things like
> the device scanning list, etc.
lvm.conf's issue_discards doesn't have any affect on the kernel (or
underlying device's) discard capabilities. It only controls whether
discards are issued by lvm for certain lvm operations (like when an LV
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