Thank you, Ian,

You are getting ZFS over 2-disk RAID-0 to be twice as fast as dd raw disk
read on one disk, which sounds more encouraging. But, there is something odd
with dd from raw drive - it is only 28MB/s or so, if I divided that right? I
would expect it to be around 100MB/s on 10K drives, or at least that should
be roughly potential throughput rate. Compared to throughput from ZFS 2-disk
RAID-0 which is showing 57MB/s. Any idea why raw dd read is so slow?

Also, I wonder if everyone is using different dd command then I am - I get
summary line that shows elapsed time and MB/s.

On 5/14/07, Ian Collins <[EMAIL PROTECTED]> wrote:

Marko Milisavljevic wrote:
> To reply to my own message.... this article offers lots of insight into
why dd access directly through raw disk is fast, while accessing a file
through the file system may be slow.
>
> http://www.informit.com/articles/printerfriendly.asp?p=606585&rl=1
>
> So, I guess what I'm wondering now is, does it happen to everyone that
ZFS is under half the speed of raw disk access? What speeds are other people
getting trying to dd a file through zfs file system? Something like
>
> dd if=/pool/mount/file of=/dev/null bs=128k (assuming you are using
default ZFS block size)
>
> how does that compare to:
>
> dd if=/dev/dsk/diskinzpool of=/dev/null bs=128k count=10000
>
>
Testing on a old Athlon MP box, two U160 10K SCSI drives.

bash-3.00# time dd if=/dev/dsk/c2t0d0 of=/dev/null bs=128k count=10000
10000+0 records in
10000+0 records out

real    0m44.470s
user    0m0.018s
sys     0m8.290s

time dd if=/test/play/sol-nv-b62-x86-dvd.iso of=/dev/null bs=128k
count=10000
10000+0 records in
10000+0 records out

real    0m22.714s
user    0m0.020s
sys     0m3.228s

zpool status
  pool: test
state: ONLINE
scrub: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        test        ONLINE       0     0     0
          mirror    ONLINE       0     0     0
            c2t0d0  ONLINE       0     0     0
            c2t1d0  ONLINE       0     0     0

Ian


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