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Re: XFS and nobarrier with SSDs

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Martin Steigerwald <martin@xxxxxxxxxxxx>
Subject: Re: XFS and nobarrier with SSDs
From: Georg Schönberger <g.schoenberger@xxxxxxxxxx>
Date: Mon, 14 Dec 2015 10:18:54 +0000
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Cc: Jens Axboe <axboe@xxxxxxxxx>, Jeff Moyer <jmoyer@xxxxxxxxxx>, Linux FS-Devel <linux-fsdevel@xxxxxxxxxxxxxxx>, Linux Block mailing list <linux-block@xxxxxxxxxxxxxxx>, XFS mailing list <xfs@xxxxxxxxxxx>
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Thread-topic: XFS and nobarrier with SSDs
On 2015-12-14 10:58, Christoph Hellwig wrote:
> On Mon, Dec 14, 2015 at 09:38:56AM +0100, Martin Steigerwald wrote:
>> Is it safe to use XFS (or any other filesystem) on enterprise SSDs with Power
>> Loss Protection (PLP), i.e. some capacitor to provide for enough electricity
>> to write out all data in DRAM to flash after a power loss, with a reordering
>> I/O scheduler like CFQ?
> If the device does not need cache flushes it should not report requiring
> flushes, in which case nobarrier will be a noop.
OK - that would also mean that mounting with nobarrier should not make a 
performance difference.

> Or to phrase it
> differently:  If nobarrier makes a difference skipping it is not safe.
I do not fully understand that sentence, what do you mean by "makes a 
difference" and "skipping is not safe"?

-Georg
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