Date: Fri, 17 Sep 2010 20:55:30 -0400 From: jhell <jhell@DataIX.net> To: Freddie Cash <fjwcash@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: what happens to pool if ZIL dies on ZFS v14 Message-ID: <4C940E02.1010405@DataIX.net> In-Reply-To: <AANLkTikEx-ZALCSOb%2Bot1CrKrK-u7rd54pQN-GjDDFVO@mail.gmail.com> References: <AANLkTi=vYVG300nhMjkcLju=kQhBdPJDqyaXR0mG84%2Bp@mail.gmail.com> <4C9385B0.2080909@shatow.net> <AANLkTin0LwQz%2BWi5cBOcHuVqyOz3%2BfFR7YC_=f2L5CyX@mail.gmail.com> <AANLkTinbPK1rNK5hg=t7N=sqFLuh8sNrZT9DFC_ppXWF@mail.gmail.com> <20100917161847.GA58503@icarus.home.lan> <AANLkTi=NX6koyj_xmadrTw8OvgCATPA=EQnTPmAxNGpo@mail.gmail.com> <AANLkTimd6ZKENg3-W-1DxOoR5mRcTb0mfRikznKWuBTD@mail.gmail.com> <AANLkTikEx-ZALCSOb%2Bot1CrKrK-u7rd54pQN-GjDDFVO@mail.gmail.com>
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On 09/17/2010 13:09, Freddie Cash wrote: > On Fri, Sep 17, 2010 at 9:47 AM, Gil Vidals <gvidals@gmail.com> wrote: >> First, let me say that I'm receiving excellent input from the FreeBSD >> community. I'm new to FreeBSD and ZFS and this mailing list has been very >> helpful. >> >> I'm running ZFSv14 on FreeBSD 8.1 AMD64 with 8GB of DDR3 RAM with two SSDs - >> one for the ZIL and the other for the L2ARC cache. >> >> zambia# zpool iostat -v 1 1 >> capacity operations bandwidth >> pool used avail read write read write >> ---------------- ----- ----- ----- ----- ----- ----- >> tank 6.57G 921G 0 11 116K 438K >> mirror 6.57G 921G 0 5 116K 229K >> label/disk1 - - 0 3 57.9K 229K >> label/disk2 - - 0 3 57.8K 229K >> label/zilcache 136K 59.5G 0 6 17 209K >> cache - - - - - - >> label/l2cache 59.6G 8.50K 0 0 31.5K 48.9K >> ---------------- ----- ----- ----- ----- ----- ----- >> >> Observing the ZIL Cache, I see it being used very sparingly. And now that I >> know the SSD slog must be mirrored in ZFS < v19, I think the best course of >> action (assuming I'm not buying more equipment) is to mirror the ZIL SSD and >> abandon the L2ARC altogether. Won't RAM be used for L2ARC instead? > > The ZIL is only used for synchronous writes, and does not need to be > very large. I forget the formula for determining the exact size of a > ZIL (something along the lines of the max amount of data you can write > in 30 seconds), but it's rarely more than 4 GB and usually in the 1-2 > GB range. > > If possible, you'd be better off rebuilding your pool like so: > mirror disk1 and disk2 > slice both SSDs into two: 4-8 GB for ZIL, rest for L2ARC > mirror zilcache1 zilcache2 > add l2cache1 l2cache2 (don't mirror them) > > That way, you have a mirrored ZIL, and double the L2ARC. However, > since it takes around 270 bytes of RAM for every object in the L2ARC, > you'll want to make sure you have lots of RAM to manage it (or, > possibly, make 3 slices on the SSDs and use the third for swap?). > http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide#Disabling_the_ZIL_.28Don.27t.29 -- jhell,v
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