I've got a system running Debian kernel 3.2.0-4-amd64 with root on a SSD that
identifies itself as "INTEL SSDSC2CT12 300i" (it's an Intel 120G device).
Here is the /proc/mounts entry which shows that ssd and discard options are
enabled.
/dev/disk/by-uuid/7939c405-c656-4e85-a6a0-29f17be09585 / btrfs
rw,seclabel,nodev,noatime,ssd,discard,space_cache 0 0
Here is the "expert mode" output of fdisk which shows that /dev/sda3 (the root
filesystem) is aligned to a multiple of 4096 sectors (surely 2MB is larger than
the erase block size although a quick Google search didn't turn up the number
for that device).
Disk /dev/sda: 255 heads, 63 sectors, 14593 cylinders
Nr AF Hd Sec Cyl Hd Sec Cyl Start Size ID
1 80 32 33 0 53 55 62 2048 997376 83
2 00 53 56 62 211 28 183 999424 1953792 82
3 00 211 29 183 254 63 1023 2953216 231487488 83
4 00 0 0 0 0 0 0 0 0 00
But I'm seeing very poor write performance, the system will block on disk IO
when iostat is reporting a few hundred KB/s in writes. Below is some output
of "iostat -x 10":
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz
avgqu-sz await r_await w_await svctm %util
sda 0.00 0.00 0.00 100.00 0.00 50.00 1.00
1.00 10.00 0.00 10.00 10.00 100.00
avg-cpu: %user %nice %system %iowait %steal %idle
27.04 0.00 3.10 0.00 0.00 69.86
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz
avgqu-sz await r_await w_await svctm %util
sda 0.00 0.80 0.00 107.70 0.00 116.75 2.17
1.04 9.66 0.00 9.66 9.28 99.96
avg-cpu: %user %nice %system %iowait %steal %idle
18.31 0.00 1.82 0.00 0.00 79.87
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz
avgqu-sz await r_await w_await svctm %util
sda 0.00 0.00 0.00 100.80 0.00 55.60 1.10
1.00 9.95 0.00 9.95 9.92 100.00
Any suggestions for how to debug or improve things?
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