Date: Tue, 15 Jun 2010 17:53:48 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Thomas Steen Rasmussen <thomas@gibfest.dk> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS l2arc and HAST ? newbie question Message-ID: <20100615155348.GA1922@garage.freebsd.pl> In-Reply-To: <4C177E69.3020204@gibfest.dk> References: <4C177E69.3020204@gibfest.dk>
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--45Z9DzgjV8m4Oswq Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Jun 15, 2010 at 03:21:45PM +0200, Thomas Steen Rasmussen wrote: > Hello list, >=20 > I am playing with HAST in order to build some redundant storage > for a mailserver, using ZFS as the filesystem. > I have the following zpool layout before stating the HAST experiments: >=20 > NAME STATE READ WRITE CKSUM > tank ONLINE 0 0 0 > raidz2 ONLINE 0 0 0 > label/hd4 ONLINE 0 0 0 > label/hd5 ONLINE 0 0 0 > label/hd6 ONLINE 0 0 0 > label/hd7 ONLINE 0 0 0 > logs ONLINE 0 0 0 > mirror ONLINE 0 0 0 > label/ssd0s1 ONLINE 0 0 0 > label/ssd1s1 ONLINE 0 0 0 > cache > label/ssd0s2 ONLINE 0 0 0 > label/ssd1s2 ONLINE 0 0 0 >=20 > As I understand it, to accomplish this with HAST I will need to make a > HAST resource for each physical disk, like so: >=20 > NAME STATE READ WRITE CKSUM > tank ONLINE 0 0 0 > raidz2 ONLINE 0 0 0 > hast/hahd4 ONLINE 0 0 0 > hast/hahd5 ONLINE 0 0 0 > hast/hahd6 ONLINE 0 0 0 > hast/hahd7 ONLINE 0 0 0 >=20 > But what about slog and cache devices, currently on SSD disks for > performance reasons ? It doesn't really make sense to synchronize > a cache disk over the network, does it ? No, it doesn't. Cache is forgotten on import anyway, so don't bother. You have to be careful, though, because you probably need to remove old cache device from the pool after import on secondary and add local disk. > Could I build the zpool with the SSD disks directly (without > HAST) and would ZFS survive an export/import on the other host, > when the cache disks are suddently different ? I am thinking cache > only here, not slog. It simply won't find cache disks, you will need to do what I described above. > Do SSD l2arc / slog even make any sense when I am "deliberately" > slowing down the filsystem with network redundancy anyway ? Forget about HAST for L2ARC. In case of SLOG it can still be faster over the network than pool with local SATA disks without SLOG. As usual the best way to verify this is to test it for your workload:) > Oh, and is there any problems using labels for HAST devices ? My > controller likes to give new device names to disks now and then, > and it has been a blessing to use labels instead of device names, > so I'd like to continue doing that when using HAST. Use labeled providers in hast.conf, but there is no need to label HAST providers (/dev/hast/<name>). --=20 Pawel Jakub Dawidek http://www.wheelsystems.com pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --45Z9DzgjV8m4Oswq Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAkwXogwACgkQForvXbEpPzRS7wCg0I8Z5JIeEzGlDKG58PhhcCGg YScAoO8oqrTiQigGDyHDm1gH1U4G8uW0 =Lkt6 -----END PGP SIGNATURE----- --45Z9DzgjV8m4Oswq--
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