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

[Damien Fleuriot]

On 1/7/11 1:10 PM, Markiyan Kushnir wrote:
> 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)?
> 
> 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.