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

Niels de Carpentier zfs at decarpentier.com
Thu Sep 19 08:25:25 EDT 2013


> On 18/09/13 20:31, bgribble at gmail.com wrote:
>> I'm also experiencing slow write behavior on ubuntu 12.04 with ZoL
>> 0.6.2. Running an 11x4TB drive raidz3 (ashift=12) connected to 2x M1015
>> flashed to IT mode with less than 6TB used i'm seeing this (xeon e5530,
>> 8GB ram, no dedup) :
>>
>> time dd if=/dev/zero of=zerofile12.tst bs=4k count=4700000
>> 4700000+0 records in
>> 4700000+0 records out
>> 19251200000 bytes (19 GB) copied, 63.74 s, 302 MB/s
>
>
> ZFS raidz* write speed on any given vdev is limited to about the maximum
> write speed of a single drive.
>
> Unless you have 15,000 rpm drives, what you're seeing is about what I'd
> expect.

No, sequential write speed scales pretty well with the number of drives,
IOPS don't. But in this case the 4k block size is likely the limiting
factor, using a larger block size should give much better results.

Niels

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