From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Mamedov Subject: Re: messed up changing chunk size Date: Mon, 19 Jul 2010 20:58:16 +0600 Message-ID: <20100719205816.222ea76e@natsu> References: <4C439D19.4070906@gmail.com> <20100719095351.4536a252@natsu> <4C4451FC.30505@oxfordinspire.co.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/0oFRqMzxceXlN+5pbk5Erae"; protocol="application/pgp-signature" Return-path: In-Reply-To: <4C4451FC.30505@oxfordinspire.co.uk> Sender: linux-raid-owner@vger.kernel.org To: Jools Wills Cc: Konstantin Svist , linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/0oFRqMzxceXlN+5pbk5Erae Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Mon, 19 Jul 2010 14:24:12 +0100 Jools Wills wrote: > >> I looked around and found that chunk size > >> of 512 should work better. > > > > Not true, at least with RAID5/6 a chunk size of 64K performs faster, see > > http://louwrentius.blogspot.com/2010/05/raid-level-and-chunk-size-bench= marks.html > > http://alephnull.com/benchmarks/sata2009/chunksize.html >=20 > There is no mention in this benchmark tests if he modified the stripe=20 > cache. With an increased stripe size a larger stripe cache would be=20 > needed for good performance (at least from my experience) That's true, but increasing the stripe cache helps across all chunk sizes, = even with relatively low 128K, see [1]. And I don't think that a large-chunk(512= K) configuration will significantly, if at all, outperform a small-chunks(64K) one at any given stripe cache size (set to the same value in both cases). There's also an opinion I heard from a couple of sources, that the stripe s= ize better be chosen so that either one stripe, or a whole stride fits inside t= he CPU's L2 or L3 cache. Sounds logical, though I am not convinced that this is what causes the performance difference between various stripe sizes. [1] http://peterkieser.com/2009/11/29/raid-mdraid-stripe_cache_size-vs-write-tr= ansfer/ --=20 With respect, Roman --Sig_/0oFRqMzxceXlN+5pbk5Erae Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iEYEARECAAYFAkxEaAgACgkQTLKSvz+PZwiVmgCfZXowCHOVnZ6kYJzuZ/dEqZwp HkUAnjNAIbvy19TWVSTP+qRhJRQscUCX =zEoe -----END PGP SIGNATURE----- --Sig_/0oFRqMzxceXlN+5pbk5Erae--