Date: Wed, 29 Jul 2009 10:19:00 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: cooper <bo.coopci@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: About RAIDZ geometry Message-ID: <20090729081900.GC1586@garage.freebsd.pl> In-Reply-To: <4A6E970A.1060503@gmail.com> References: <4A6E970A.1060503@gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
--nFreZHaLTZJo0R7j Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Jul 28, 2009 at 02:13:30PM +0800, cooper wrote: > Hi folks, >=20 > Now that ZFS has been ported to FreeBSD, I think it's proper to ask > these questions in this mailing list. >=20 > Is there any detailed documentation about RAIDZ geometry? I has been > wandering how zfs remembers which disk sectors are for data and which > ones are for parity. >=20 > They claimed "Every block is its own RAID-Z stripe" does that mean zfs > writes exactly one block in every vdev_raidz_io_start if the io type of > the zio is write? >=20 > And also claimed "You have to traverse the filesystem metadata to > determine the RAID-Z geometry" where is this metadata stored? If you have file system separated from volume manager doing RAID, the volume manager has no knowledge where the live data is, etc. Imagine a ZFS 5-disks RAIDZ1 configuration: disk0 disk1 disk2 disk3 disk4 ZFS' file system level wants to store two sectors of data so it sends 1kB of data to lower ZFS layers. You then get something like this: disk0 disk1 disk2 disk3 disk4 data0 data1 parity01 Now ZFS wants to store one sector and you get this: disk0 disk1 disk2 disk3 disk4 data0 data1 parity01 data2 parity2 ZFS can do that, because he knows where and how to read the data back (its a file system and volume manager). ZFS will never try to read three sectors as one block of data. This is impossible to do when file system is separated from volume manager. --=20 Pawel Jakub Dawidek http://www.wheel.pl pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --nFreZHaLTZJo0R7j Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQFKcAX0ForvXbEpPzQRAoRMAJ0arT2tov9eIAdAXWCsAkmCvEAn8ACZAfEQ s3m4ujNZFoXS9vTiJ8ylK08= =VROf -----END PGP SIGNATURE----- --nFreZHaLTZJo0R7j--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20090729081900.GC1586>