Date: Thu, 28 Dec 2006 19:24:45 +0100 From: Ivan Voras <ivoras@fer.hr> To: freebsd-geom@freebsd.org Subject: Re: gstripe performance scaling with many disks Message-ID: <en125k$l2e$1@sea.gmane.org> In-Reply-To: <20061228171858.GA11296@qlovarnika.bg.datamax> References: <20061228171858.GA11296@qlovarnika.bg.datamax>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig9A7097DADAAF2593CDBF794C Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Vasil Dimov wrote: > Can someone explain this? > The tendency is for performace drop when increasing the number of disks= > in a stripe but there are some local peaks/extremums when using 8, 11 > and 16 disks. I'll take a shot at this: Since maximum kernel reads are still limited to 128 KB/s, by adding more drives you're making individual requests shorter. I.e. with one drive, it gets 128 KB requests, with two, each gets 64 KB, with 16, each gets 8 KB. So network & kernel latency becomes visible. AFAIK there's unofficial (still?) GEOM_CACHE class which tries to get around this by requesting & caching 128K from each drive. Search the lists, it's mentioned somewhere. >=20 > Yes, I have read > http://lists.freebsd.org/pipermail/freebsd-geom/2006-November/001705.ht= ml >=20 > kern.geom.stripe.fast is set to 1. While you're playing with this, you could set vfs.read_max to 32 or higher and see if it helps. --------------enig9A7097DADAAF2593CDBF794C Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.4 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFlAvzldnAQVacBcgRApOtAKDPqJ/HJfmf6M6jvctjitjzfkHVsgCgv59d ftyB+tS4eELnv1k02rWxpTM= =sgLO -----END PGP SIGNATURE----- --------------enig9A7097DADAAF2593CDBF794C--
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