ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks

Markiyan Kushnir markiyan.kushnir at gmail.com
Fri Jan 7 12:33:42 UTC 2011

2011/1/7 Jeremy Chadwick <freebsd at 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 at 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)?


> I tried this, but couldn't get rc.d/mdconfig2 to do what I wanted on
> startup WRT the aforementioned.
> --
> | Jeremy Chadwick                                   jdc at parodius.com |
> | Parodius Networking                       http://www.parodius.com/ |
> | UNIX Systems Administrator                  Mountain View, CA, USA |
> | Making life hard for others since 1977.               PGP 4BD6C0CB |
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