On 06/04/2013 05:39 PM, Joe Lawrence wrote:

Just curious, what type drives were in your RAID and what does
/sys/class/scsi_disk/*/max_write_same_blocks report?  If you have a spare
drive to test, maybe you could try a quick sg_write_same command to see
how the drive reacts?

I just run into the same issue with an ancient system from 2006. Except 
that I'm in hurry an need it to stress-test my own work, I can do 
anything with it - it is booted via NFS and disks are only used for 
development/testing.

(squeeze)fslab1:~# cat /sys/block/md126/queue/write_same_max_bytes
16384

(squeeze)fslab1:~# cat /sys/block/sd[o,n,m,l]/queue/write_same_max_bytes
0
0
0
0

Ah, now I found the reason why it fails, scsi-layer had set 
write_same_max_bytes to zero when it detected that it does not support 
it, but after reloading the arecal module (arcmsr) I now get:

(squeeze)fslab1:~# cat /sys/block/sd[o,n,m,l]/queue/write_same_max_bytes
33553920
33553920
33553920
33553920

Now for example

11:0:1:2]   disk    Hitachi  HDS724040KLSA80  R001  /dev/sdl  /dev/sg11

(squeeze)fslab1:~# sg_write_same --num=100 /dev/sg11
Write same(10) command not supported

(squeeze)fslab1:~# sg_write_same --16 --num=100 /dev/sg11
Write same(16) command not supported

Cheers,
Bernd


PS: This is the 2nd time this I run into this, on Sunday I had a similar 
same issue at home with Ubuntus 3.8 kernel, but somehow not with vanilla 
3.9. I need to recheck the logs in evening to see if it is really the 
same issue.