Date: Mon, 6 Oct 2008 08:25:47 +0300 From: "Dimitar Vasilev" <dimitar.vassilev@gmail.com> To: "Andrew Snow" <andrew@modulus.org> Cc: freebsd-fs@freebsd.org Subject: Re: zfs as layer distributor Message-ID: <59adc1a0810052225w6d8c1b78r226ffe8ca4ccf35d@mail.gmail.com> In-Reply-To: <48E9556C.9060004@modulus.org> References: <59adc1a0810051210t4a3503aci2bc06ba0aa5376c3@mail.gmail.com> <48E9556C.9060004@modulus.org>
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2008/10/6 Andrew Snow <andrew@modulus.org> > Dimitar Vasilev wrote: > >> Hi all, >> Does someone use zfs as layer distributor on the top of hardware raid - >> (RAID10,RAID6,etc)? >> > > I've found ZFS works faster when given more than one disk device. The > reason being, it is smart about writing journal logs and metadata copies to > different devices, resulting in higher performance by using idle disks. It > also provides more "channels" for write clustering so higher throughput on > write-heavy loads. > > Secondly if you use ZFS to provide RAID1 or RAID5, due to checksumming it > can be smarter about which data it chooses in the event of a checksum > failure. Hardware RAID can only do this with RAID6. > > Finally, when ZFS issues "flush cache" command to the disk for metadata and > journal logs, there is less data to flush when you give it multiple smaller > devices. If you have a single monolithic RAID device with a large (eg. > 256mb) cache, it can ruin performance while the RAID card flushes its entire > cache. (This can be disabled with a sysctl). > > - Andrew Thanks Andrew, I have an Areca 1120 with RAID-6 and on the top of it a zfs as a layer distributor. So far I can tell the following: 1)works nice and fast 2)can be pain in the rear if your controller spits one of the disks due to power surge/etc. 3) zfs snapshots caused some crashes and bad descriptors on 7.0-stable as of 3 months behind- but it's somewhat expected. I'm thinking of raidz2 and setting the disks as pass-through. Would love if someone to hear if someone has tested hardware raid6 and zfs over it. Best regards, Dimitar
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