Date: Mon, 13 May 2013 08:40:55 -0400 From: Paul Kraus <paul@kraus-haus.org> To: =?windows-1252?Q?Trond_Endrest=F8l?= <Trond.Endrestol@fagskolen.gjovik.no> Cc: "freebsd-questions@freebsd.org List" <freebsd-questions@freebsd.org> Subject: Re: ZFS mirror install /mnt is empty Message-ID: <472E17AF-B249-4FD3-8F5E-716F8B7867F5@kraus-haus.org> In-Reply-To: <alpine.BSF.2.00.1305130743320.72982@mail.fig.ol.no> References: <5190058D.2030705@micite.net> <alpine.BSF.2.00.1305130743320.72982@mail.fig.ol.no>
next in thread | previous in thread | raw e-mail | index | archive | help
On May 13, 2013, at 1:58 AM, Trond Endrest=F8l = <Trond.Endrestol@fagskolen.gjovik.no> wrote: > Due to advances in hard drive technology, for the worse I'm afraid,=20 > i.e. 4K disk blocks, I wouldn't bother enabling compression on any ZFS=20= > file systems. I might change my blog posts to reflect this stop gap. >=20 > If you do happen to have 4K drives, you might want to check out this=20= > blog post: >=20 > = https://ximalas.info/2012/01/11/new-server-and-first-attempt-at-running-fr= eebsdamd64-with-zfs-for-all-storage/ I did look, it doesn't explain why not to enable compression on = 4k sector drives. =46rom discussion on the zfs-discuss lists (both the old one = from OpenSolaris and the new one at Illumos) the only issue with 4K = sector drives is mixing 0.5K sector and 4K sector drives. You can tunes = the zpool offset to handle 4K sector drives just fine, but it is a pool = wide tuning. http://zfsday.com/wp-content/uploads/2012/08/Why-4k_.pdf has = some 4K background, and the only mention I see of compression and 4K is = that you may get less. But=85 you really need to test your data to see = if turning compression on is beneficial with any dataset. There is = noticeable computational overhead to enabling compression. If you are = CPU bound, then you will get better performance with compression off. If = you are limited by the I/O bandwidth to your drives, then *if* your data = is highly compressible, then you will get better performance with = compression on. I have managed large pools of both data that compresses = well and data that does not. = http://wiki.illumos.org/display/illumos/ZFS+and+Advanced+Format+disks = discusses the issue and presents solutions using Illumos. I could find = no such examples for FreeBSD, but I'm sure some of the same techniques = would work (manually setting the ashift to 12 for 4K disks). -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?472E17AF-B249-4FD3-8F5E-716F8B7867F5>