27.08.2012 14:02, Sašo Kiselkov пишет:

Can someone with Supermicro JBOD equipped with SAS drives and LSI
HBA do this sequential read test?


Did that on a SC847 with 45 drives, read speeds around 2GB/s aren't a
problem.
Thanks for info.

Don't forget to set primarycache=none on testing dataset.

There's your problem. By disabling the cache you've essentially
disabled prefetch. Why are you doing that?

Hm. The box have 96Gb RAM. I tried to exclude influence ARC cache.
Hasn't  thought about prefetch...

readspeed is:
readspeed ()  { dd if=$1 of=/dev/null bs=1M ;}


root@atom:/sas1/test# zfs set primarycache=metadata sas1/test
root@atom:/sas1/test# readspeed 3g
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 19.2203 s, 164 MB/s

Prefetch still disabled?

root@atom:/sas1/test# zfs set  primarycache=all sas1/test
root@atom:/sas1/test# readspeed 3g
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 3.99195 s, 788 MB/s

Seems to be this is disk read speed with prefetch enabled.

root@atom:/sas1/test# readspeed 3g
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 0.901665 s, 3.5 GB/s
root@atom:/sas1/test# readspeed 3g
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 1.02127 s, 3.1 GB/s
root@atom:/sas1/test# readspeed 3g
3000+0 records in
3000+0 records out
3145728000 bytes (3.1 GB) copied, 0.86884 s, 3.6 GB/s

These results  obviously are from memory.

Is there any way to disable ARC for testing and leave prefetch enabled?



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