vfs.zfs.prefetch_disable="1" causes much slow read on sequence data in my
case.
with vfs.zfs.prefetch_disable="1":
dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500
524288000 bytes transferred in 18.347177 secs (28575949 bytes/sec)
with vfs.zfs.prefetch_disable="0":
dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500
524288000 bytes transferred in 3.331806 secs (157358504 bytes/sec)
after few seconds:
dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500
524288000 bytes transferred in 0.107767 secs (4865009592 bytes/sec)
My system:
FreeBSD 8.2-RELEASE
hw.machine: amd64
hw.model: Intel(R) Xeon(R) CPU E5520 @ 2.27GHz
hw.ncpu: 8
hw.physmem: 17155719168
3ware 9690sa controller
Disks: ST32000445SS
pool: pool1
NAME STATE READ WRITE CKSUM
pool1 ONLINE 0 0 0
raidz2 ONLINE 0 0 0
da12 ONLINE 0 0 0
da11 ONLINE 0 0 0
da10 ONLINE 0 0 0
da9 ONLINE 0 0 0
da16 ONLINE 0 0 0
da15 ONLINE 0 0 0
da14 ONLINE 0 0 0
da13 ONLINE 0 0 0
--
Best regards,
Sergey Gavrilov
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