On Tue, Apr 12 2011 at 9:47pm -0400,
DarkNovaNick@xxxxxxxxx <DarkNovaNick@xxxxxxxxx> wrote:
> I get 0 back when I do "cat
> /sys/block/sda/queue/discard_zeroes_data" so does this mean that my
> drive doesn't zero out the TRIMed blocks? I don't really care if it
> does or does not, I just want to make sure the drive is getting the
> TRIM commands as the benchmarks I've seen show performance
> degradation if they aren't used.
Right, means TRIM doesn't zero the TRIM'd blocks.
But otherwise it looks like you're in good shape relative to TRIM.
> Regarding snapshot targets, the only instance of "discard not
> supported" came as I did a snapshot today:
>
> Apr 12 15:27:58 darknovanick kernel: [65147.211211] EXT4-fs warning
> (device dm-0): release_blocks_on_commit:2672: discard not supported,
> disabling
> Apr 12 15:28:16 darknovanick kernel: [65166.103061] EXT4-fs (dm-1):
> 72 orphan inodes deleted
> Apr 12 15:28:16 darknovanick kernel: [65166.103062] EXT4-fs (dm-1):
> recovery complete
> Apr 12 15:28:17 darknovanick kernel: [65166.232257] EXT4-fs (dm-1):
> mounted filesystem with ordered data mode. Opts: (null)
>
> This snapshot was of a LV on the SSD, but the snapshot itself was
> being stored on a mechanical hard drive. Does this message mean that
> discard was just disabled for the snapshot itself (which was deleted
> a half hour later), or is it now disabled for the entire volume now
> that I've done a snapshot, even though its been removed?
Unfortunately, the failed discard to the snapshot-origin device disables
ext4's discards for the entire volume (even after you remove the
snapshot).
But the following patch fixes that:
Subject: dm snapshot: add discard support to the snapshot-origin target
Allow the snapshot-origin target to pass discards to the origin device
(after any copyout of the region being discarded; but generally speaking
that copyout won't be needed as the region will have already been copied
to the cow).
So for example, when you remove a file from an ext4 mounted origin
volume it triggers copyout to the snapshot. When the DISCARD is then
issued during the subsequent journal commit no copyout is needed.
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
drivers/md/dm-snap.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index a2d3309..028d216 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -2076,6 +2076,7 @@ static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
ti->private = dev;
ti->num_flush_requests = 1;
+ ti->num_discard_requests = 1;
return 0;
}
@@ -2153,7 +2154,7 @@ static int origin_iterate_devices(struct dm_target *ti,
static struct target_type origin_target = {
.name = "snapshot-origin",
- .version = {1, 7, 1},
+ .version = {1, 8, 0},
.module = THIS_MODULE,
.ctr = origin_ctr,
.dtr = origin_dtr,
--
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