From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Mamedov Subject: Re: Write-intent bitmap decreases or increase performance of RAID5? Date: Fri, 2 Jul 2010 02:49:27 +0600 Message-ID: <20100702024927.21c4f814@natsu> References: <20100629201153.GA13018@localhost> <20100630111854.006ec4d0@natsu> <20100701064044.GB6058@localhost> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/n=H9OjXWbleMEIS.1pvMi.G"; protocol="application/pgp-signature" Return-path: In-Reply-To: <20100701064044.GB6058@localhost> Sender: linux-raid-owner@vger.kernel.org To: Shaochun Wang Cc: "linux-raid@vger.kernel.org" List-Id: linux-raid.ids --Sig_/n=H9OjXWbleMEIS.1pvMi.G Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Thu, 1 Jul 2010 14:40:44 +0800 Shaochun Wang wrote: > -bash-4.1$ sudo dd if=3D/dev/zero of=3Dtest.dd bs=3D1M count=3D5000 > conv=3Dfdatasync,notrunc Password: > 5000+0 records in > 5000+0 records out > 5242880000 bytes (5.2 GB) copied, 63.497 s, 82.6 MB/s >=20 > -bash-4.1$ sudo dd if=3D/dev/zero of=3Dtest.dd bs=3D1M count=3D5000 > conv=3Dfdatasync,notrunc 5000+0 records in > 5000+0 records out > 5242880000 bytes (5.2 GB) copied, 18.1033 s, 290 MB/s > =09 > I don't know why the second dd becomes 290MB/s and the first 82.6MB/s. That's because the first time the filesystem had to increase the file's size 5000 times by allocating additional 1 MB, and the second time it was just writing to an already allocated file. If you see such a big difference here, run that test 3 or more times, and discard the first run's results. --=20 With respect, Roman --Sig_/n=H9OjXWbleMEIS.1pvMi.G Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iEYEARECAAYFAkws/1cACgkQTLKSvz+PZwiZUQCfSda6ruOIjNHbmAqJqCFDsTB6 AtYAn0u72Wb6+U+SaidO1Y0/VZfQyDwe =C0MF -----END PGP SIGNATURE----- --Sig_/n=H9OjXWbleMEIS.1pvMi.G--