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

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Message-ID: <4BBE059D.3080208@redhat.com>
Date:	Thu, 08 Apr 2010 11:34:37 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Nebojsa Trpkovic <trx.lists@...il.com>
CC:	linux-ext4@...r.kernel.org
Subject: Re: "data=writeback" and TRIM don't get along

Nebojsa Trpkovic wrote:
> 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 ?

I think the answer is "not yet but it's being worked on"

-Eric
 
> Nebojsa

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