[zfs-discuss] Re: Moderate write speeds on Ubuntu

magnawave at gmail.com magnawave at gmail.com
Wed Sep 18 12:03:03 EDT 2013

I'd be tempted to look at the iostat data for the drives - during the 
writes, and see if the physical platters are busy with the writes.  That 
would help determine where the bottleneck is.  Its possible there is 
seeking or something else going on.   (for example I tested ZFS on Linux 
once upon a time on an LVM partition and with the LVM journalling seeking 
and the ZFS journalling, the write performance was terrible - but that's 
because the disks WERE busy seeking with the conflicting sync seeks)

For what its worth, I use the same OS release and have no problem 
saturating GigE(~110MB/s) doing fileserver writes via AFP with ZFS on Linux.

On Thursday, September 12, 2013 8:53:57 AM UTC-5, sanma... at gmail.com wrote:
> I set up 4 2TB drives,mirrored in pairs, with ZFS. I get good 200+MB read 
> speeds semi-consistently, more than enough for me, but my write speeds are 
> always down in the 40-50 MB area, which if I remember my drive benchmarks 
> correctly, is comparable to just one of the drives running by itself. I 
> understand that because I'm mirroring I won't get as dramatic of an 
> increase as my read speed, but since ZFS is striping across the two mirror 
> pairs, shouldn't I see some increase?
> I'm not familiar enough with ZFS' tools yet to perform diagnoses on what 
> may or may not be wrong here. Does anyone have any tips/commands I can try?

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