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Re: Problem about very high Average Read/Write Request Time

To: quanjun hu <huquanjun@xxxxxxxxx>
Subject: Re: Problem about very high Average Read/Write Request Time
From: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>
Date: Sat, 18 Oct 2014 14:38:48 +0200
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <CALSoAzD4ccHXBuD6mT3ggqMf1j_kDEK-RNMOeRLq+N+NiWVQXg@xxxxxxxxxxxxxx>
Organization: Intellique
References: <CALSoAzD4ccHXBuD6mT3ggqMf1j_kDEK-RNMOeRLq+N+NiWVQXg@xxxxxxxxxxxxxx>
Le Sat, 18 Oct 2014 17:26:40 +0800 vous Ãcriviez:

> Hi,
>    I am using xfs on a raid 5 (~100TB) and put log on external ssd
> device, the mount information is:
> /dev/sdc on /data/fhgfs/fhgfs_storage type xfs
> (rw,relatime,attr2,delaylog,logdev=/dev/sdb1,sunit=512,swidth=15872,noquota).
>   when doing only reading / only writing , the speed is very
> fast(~1.5G), but when do both the speed is very slow (100M), and high
> r_await(160) and w_await(200000).

What are your kernel version, mount options and xfs_info output ?

>    1. how can I reduce average request time?
>    2. can I use ssd as write/read cache for xfs?

Sure, using bcache and other similar tools.

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