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Re: XFS over SSD

To: Raz <raziebe@xxxxxxxxx>
Subject: Re: XFS over SSD
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Mon, 08 Dec 2008 09:50:55 -0600
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <5d96567b0812080711x34bb93d6vd8e4f88d9b190e9@xxxxxxxxxxxxxx>
References: <5d96567b0812080442r131d9fc8t4019c99ffbffa290@xxxxxxxxxxxxxx> <493D334C.5010006@xxxxxxxxxxx> <5d96567b0812080711x34bb93d6vd8e4f88d9b190e9@xxxxxxxxxxxxxx>
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Raz wrote:
> On Mon, Dec 8, 2008 at 4:46 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote:
>> Raz wrote:
>>> I am thinking of using XFS over a SSD disk.
>>> 1. Can I separate xfs meta data ( not just the logging) from the SSD ?
>>> can I put the meta on a different disk ?
>> Are you talking about just the log (see the mkfs man page for external
>> logs, as Justin suggested) or all metadata?  For the latter, using the
>> realtime subvolume does accomplish this (data on one volume, metadata on
>> the other) but that's not used very often.
>>
>> -Eric
>>
> I am referring to all the meta data. 128K of erase block for some block map
> update is a big penalty. I do not like much rt volumes. I tried that and it is
> cumbersome. UBIFS cannot handle 80GB Flash disks ( well, they say it is up to
> 16GB in MTD web site) . I am about to start benchmarking the SSD with XFS
> ( versus raw access ) and see how performance degrades, in read and writes.
> If there was a way to set XFS meta data ( superblocks, allocation groups...
> on a different device) it would have been nice, since we plan to use the SSD
> as a fast IO device and data persistence is not the main thing here.
> 
> we use XFS on all our SATA based servers, we tweak it ( extents and
> raid awareness).
> XFS proved to be the fastest file system for appliances that use
> Multimedia files
> and big IOs ( 1MB).
> 

I have yet to play with xfs on ssd, but I would imagine that setting up
the fs geometry to match the ssd preferred IO sizes and/or erase block
sizes might at least help.

-Eric

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