From: Brad Campbell <brad-+nnirC7rrGZibQn6LdNjmg@public.gmane.org>
To: James Harper <james.harper-NMzNsA1hOHcW+bLBXbPJGg@public.gmane.org>
Cc: "linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: how much of ssd to use?
Date: Sat, 02 Mar 2013 15:02:48 +0800 [thread overview]
Message-ID: <5131A418.3080105@fnarfbargle.com> (raw)
In-Reply-To: <6035A0D088A63A46850C3988ED045A4B3876B655-mzsoxcrO4/2UD0RQwgcqbDSf8X3wrgjD@public.gmane.org>
On 02/03/13 14:19, James Harper wrote:
> I've read that SSD drives work best when you only use some percentage of them (75%, 50%, etc) because by leaving unused space it allows the SSD more headroom to shuffle data around internally to keep things optimal. Those articles are most likely written for a filesystem on an OS that might not know about TRIM/UNMAP etc.
>
> Has anyone done any testing on sustained random write throughput on a (say) 60GB flash drive with only 50% dedicated to bcache, or 75%, or 100%?
>
SSD's use spare space to shuffle things around so they can reclaim space
freed in sizes less than a full erase block. Bcache explicitly uses big
buckets in such a way as to remove the requirement for this. Nothing is
freed in a way that would cause fragmentation of the sector space, so no
re-organising is required on the part of the drive.
prev parent reply other threads:[~2013-03-02 7:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-02 6:19 how much of ssd to use? James Harper
[not found] ` <6035A0D088A63A46850C3988ED045A4B3876B655-mzsoxcrO4/2UD0RQwgcqbDSf8X3wrgjD@public.gmane.org>
2013-03-02 7:02 ` Brad Campbell [this message]
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