Date: Fri, 07 Jan 2011 13:59:30 +0100 From: Damien Fleuriot <ml@my.gd> To: freebsd-stable@freebsd.org Subject: Re: ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks Message-ID: <4D270E32.30801@my.gd> In-Reply-To: <AANLkTikaz523zMxKzKe%2BMUoxeS4p=X2Vt0Sm6X_%2BKCsV@mail.gmail.com> References: <4D1C6F90.3080206@my.gd> <ifsia5$5ub$2@dough.gmane.org> <4D21E679.80002@my.gd> <84882169-0461-480F-8B4C-58E794BCC8E6@my.gd> <BEBC15BA440AB24484C067A3A9D38D7E0149F32D13E3@server7.acsi.ca> <488AE93A-97B9-4F01-AD0A-0098E4B329C3@my.gd> <AANLkTimezasVY%2BMJjWn2T9sBGQV-JrNmYqRwv_gPYPJP@mail.gmail.com> <CC37553B-EE13-4B5B-AC87-80D0ECC1A2B3@my.gd> <BEBC15BA440AB24484C067A3A9D38D7E0149F32D33F9@server7.acsi.ca> <AANLkTikfb7XzCfjetZYK016RoRG3JSs-%2BwiaaoCPTG8q@mail.gmail.com> <20110107014249.GA3719@icarus.home.lan> <AANLkTikaz523zMxKzKe%2BMUoxeS4p=X2Vt0Sm6X_%2BKCsV@mail.gmail.com>
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On 1/7/11 1:10 PM, Markiyan Kushnir wrote: > 2011/1/7 Jeremy Chadwick <freebsd@jdc.parodius.com>: >> On Fri, Jan 07, 2011 at 12:29:17PM +1100, Jean-Yves Avenard wrote: >>> On 6 January 2011 22:26, Chris Forgeron <cforgeron@acsi.ca> wrote: >>>> You know, these days I'm not as happy with SSD's for ZIL. I may blog about some of the speed results I've been getting over the last 6mo-1yr that I've been running them with ZFS. I think people should be using hardware RAM drives. You can get old Gigabyte i-RAM drives with 4 gig of memory for the cost of a 60 gig SSD, and it will trounce the SSD for speed. >>>> >>>> I'd put your SSD to L2ARC (cache). >>> >>> Where do you find those though. >>> >>> I've looked and looked and all references I could find was that >>> battery-powered RAM card that Sun used in their test setup, but it's >>> not publicly available.. >> >> DDRdrive: >> http://www.ddrdrive.com/ >> http://www.engadget.com/2009/05/05/ddrdrives-ram-based-ssd-is-snappy-costly/ >> >> ACard ANS-9010: >> http://techreport.com/articles.x/16255 >> >> GC-RAMDISK (i-RAM) products: >> http://us.test.giga-byte.com/Products/Storage/Default.aspx >> >> Be aware these products are absurdly expensive for what they offer (the >> cost isn't justified), not to mention in some cases a bottleneck is >> imposed by use of a SATA-150 interface. I'm also not sure if all of >> them offer BBU capability. >> >> In some respects you might be better off just buying more RAM for your >> system and making md(4) memory disks that are used by L2ARC (cache). >> I've mentioned this in the past (specifically "back in the days" when >> the ARC piece of ZFS on FreeBSD was causing havok, and asked if one >> could work around the complexity by using L2ARC with md(4) drives >> instead). >> > > Once you have got extra RAM, why not just reserve it directly to ARC > (via vm.kmem_size[_max] and vfs.zfs.arc_max)? > > Markiyan. > I haven't calculated yet but perhaps SSDs are cheaper by the GB than raw RAM. Not to mention DIMM slots are usually scarce, disk ones aren't.
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