Date: Mon, 06 Oct 2008 11:01:48 +1100 From: Andrew Snow <andrew@modulus.org> To: Dimitar Vasilev <dimitar.vassilev@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: zfs as layer distributor Message-ID: <48E9556C.9060004@modulus.org> In-Reply-To: <59adc1a0810051210t4a3503aci2bc06ba0aa5376c3@mail.gmail.com> References: <59adc1a0810051210t4a3503aci2bc06ba0aa5376c3@mail.gmail.com>
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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
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