Date: Thu, 3 Sep 2009 10:21:06 +1000 From: Emil Mikulic <emikulic@gmail.com> To: Alexander Motin <mav@FreeBSD.org> Cc: "Derek \(freebsd lists\)" <482254ac@razorfever.net>, FreeBSD-Current <freebsd-current@freebsd.org> Subject: Re: siis/atacam/ata/gmirror 8.0-BETA3 disk performance Message-ID: <20090903002106.GB17538@dmr.ath.cx> In-Reply-To: <4A9E8677.1020208@FreeBSD.org> References: <h7lmvl$ebq$1@FreeBSD.cs.nctu.edu.tw> <4A9E8677.1020208@FreeBSD.org>
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On Wed, Sep 02, 2009 at 05:51:35PM +0300, Alexander Motin wrote: > To completely load gmirror on read operations, you may need to run > two dd's same time. Also make sure, that your gmirror runs in > round-robin mode. Default split mode, which should help with linear > read, is IMHO ineffective, at least with default MAXPHYS and slice > values. On that note, there is an excellent patch in this PR which improves the way gmirror schedules read requests to different disks: http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/113885 Could someone please commit this? With this patch and a two-way mirror, I can run two linear scans of different files in parallel and get almost perfect scaling. (result: this approximately halves the wall-clock time it takes to do a backup of some fat VM images) IIRC, without the patch it's faster to run them sequentially. :( --Emil
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