Date: Tue, 16 Jul 2013 10:49:42 -0700 From: aurfalien <aurfalien@gmail.com> To: Shane Ambler <FreeBSD@ShaneWare.Biz> Cc: freebsd-questions@freebsd.org Subject: Re: to gmirror or to ZFS Message-ID: <C13CC733-E366-4B54-8991-0ED229932787@gmail.com> In-Reply-To: <51E51558.50302@ShaneWare.Biz> References: <4DFBC539-3CCC-4B9B-AB62-7BB846F18530@gmail.com> <alpine.BSF.2.00.1307152211180.74094@wonkity.com> <976836C5-F790-4D55-A80C-5944E8BC2575@gmail.com> <51E51558.50302@ShaneWare.Biz>
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On Jul 16, 2013, at 2:41 AM, Shane Ambler wrote: > On 16/07/2013 14:41, aurfalien wrote: >>=20 >> On Jul 15, 2013, at 9:23 PM, Warren Block wrote: >>=20 >>> On Mon, 15 Jul 2013, aurfalien wrote: >>>=20 >>>> ... thats the question :) >>>>=20 >>>> At any rate, I'm building a rather large 100+TB NAS using ZFS. >>>>=20 >>>> However for my OS, should I also ZFS or simply gmirror as I've a >>>> dedicated pair of 256GB SSD drives for it. I didn't ask for SSD >>>> sys drives, this system just came with em. >>>>=20 >>>> This is more of a best practices q. >>>=20 >>> ZFS has data integrity checking, gmirror has low RAM overhead. >>> gmirror is, at present, restricted to MBR partitioning due to >>> metadata conflicts with GPT, so 2TB is the maximum size. >>>=20 >>> Best practices... depends on your use. gmirror for the system >>> leaves more RAM for ZFS. >>=20 >> Perfect, thanks Warren. >>=20 >> Just what I was looking for. >=20 > I doubt that you would save any ram having the os on a non-zfs drive = as > you will already be using zfs chances are that non-zfs drives would = only > increase ram usage by adding a second cache. zfs uses it's own cache > system and isn't going to share it's cache with other system managed > drives. I'm not actually certain if the system cache still sits above > zfs cache or not, I think I read it bypasses the traditional drive = cache. >=20 > For zfs cache you can set the max usage by adjusting vfs.zfs.arc_max > that is a system wide setting and isn't going to increase if you have > two zpools. >=20 > Tip: set the arc_max value - by default zfs will use all physical ram > for cache, set it to be sure you have enough ram left for any services > you want running. >=20 > Have you considered using one or both SSD drives with zfs? They can be > added as cache or log devices to help performance. > See man zpool under Intent Log and Cache Devices. This is a very interesting point. In terms if SSDs for cache, I was planning on using a pair of Samsung = Pro 512GB SSDs for this purpose (which I haven't bought yet). But I tire of buying stuff, so I have a pair of 40GB Intel SSDs for use = as sys disks and several Intel 160GB SSDs lying around that I can = combine with the existing 256GB SSDs for a cache. Then use my 36x3TB for the beasty NAS. - aurf
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