linux-ext4 - Re: "data=writeback" and TRIM don't get along

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Date:	Thu, 08 Apr 2010 18:21:49 +0200
From:	Nebojsa Trpkovic <trx.lists@...il.com>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	linux-ext4@...r.kernel.org
Subject: Re: "data=writeback" and TRIM don't get along

On 04/08/10 17:32, Eric Sandeen wrote:
> Well, you might just keep in mind that:
> 
> 1) trimming these small amounts has actually looked very inefficient, and
> 2) data=writeback really isn't very safe in the face of a crash or power loss, and
> 3) hopefully we'll have a better trim solution eventually.

1) I understand that big TRIMs are better then small ones, but skipping
some TRIMs completely would lead to slow but sure drive degradation as
drive would have less and less spare space for wear leveling.

2) Yes, I'm aware of possible data=writeback inconsistency, but I've
tried to let IO scheduler to merge and reorganize as many writes as it
can, all to avoid small writes to SSD which are main cause of write
amplification.

3) I'll stick with no data=writeback for the time being. I guess I'm
doing just fine even without it. :)

One more noob quotestion completely out-of-topic:
Will md layer pass TRIM command to drive if one has ext4 on linux
software RAID 0/1/5 ?

Nebojsa
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