[Gluster-users] Slow on writing

[Anand Avati]

On Sat, Aug 17, 2013 at 5:20 AM, Jeff Darcy <jdarcy at redhat.com> wrote:

> On 08/16/2013 11:21 PM, Alexey Shalin wrote:
>
>> I wrote small script :
>> #!/bin/bash
>>
>> for i in {1..1000}; do
>> size=$((RANDOM%5+1))
>> dd if=/dev/zero of=/storage/test/bigfile${i} count=1024 bs=${size}k
>> done
>>
>> This script creates files with different size on volume
>>
>> here is output:
>> 2097152 bytes (2.1 MB) copied, 0.120632 s, 17.4 MB/s
>> 1024+0 records in
>> 1024+0 records out
>> 1048576 bytes (1.0 MB) copied, 0.14548 s, 7.2 MB/s
>> 1024+0 records in
>> 1024+0 records out
>>
>
> It looks like you're doing small writes (1-6KB) from a single thread.
>  That means network latency is going to be your primary limiting factor.
>  20MB/s at 4KB is 5000 IOPS or 0.2ms per network round trip.  You don't say
> what kind of network you're using, but if it's Plain Old GigE that doesn't
> seem too surprising.  BTW, the NFS numbers are likely to be better because
> the NFS client does more caching and you're not writing enough to fill
> memory, so you're actually getting less durability than in the
> native-protocol test and therefore the numbers aren't directly comparable.
>
> I suggest trying larger block sizes and higher I/O thread counts (with
> iozone you can do this in a single command instead of a script).  You
> should see a pretty marked improvement.
>
>
Also, small block size writes kill performance on FUSE because of the
context switches (and lack of write caching in FUSE). Larger block size (>=
64KB) should start showing good performance.

Avati
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