linux-kernel - Re: New TRIM/UNMAP tree published (2009-05-02)

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Date:	Mon, 04 May 2009 15:23:56 +0000
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	dgilbert@...erlog.com
Cc:	Jeff Garzik <jeff@...zik.org>, Matthew Wilcox <matthew@....cx>,
	Jens Axboe <jens.axboe@...cle.com>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Hugh Dickins <hugh@...itas.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Mark Lord <lkml@....ca>
Subject: Re: New TRIM/UNMAP tree published (2009-05-02)

On Mon, 2009-05-04 at 17:11 +0200, Douglas Gilbert wrote:
> Another aspect, especially if a large amount of storage
> is to be trimmed, is how long will it take? This relates
> to the timeout value we should associate with such an
> invocation. The FORMAT UNIT and START STOP UNIT commands
> have an IMMED bit, but not WRITE SAME.

I was assuming it would be more or less instantaneous ... if it's not
then the plan of trying to keep thin provisioning happy just by sending
down a maximal trim from the filesystem is going to run into trouble.

> Speaking of FORMAT UNIT, some words were added into sbc3r18
> that suggest a FORMAT UNIT command could be interpreted as
> unmap/trim the whole disk.

Seems reasonable ... if you format the device it could be argued you're
not relying on the data contents any more ...

James


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