Hi, I have been doing some basic performance tests, and I am getting a big hit when I run UFS over a zvol, instead of directly using zfs. Any hints or explanations is very welcome. Here's the scenario. The machine has 30G RAM, and two IDE disks attached. The disks have 2 fdisk partitons (c4d0p2, c3d0p2) that are mirrored and form a zpool. When using filebench with 20G files writing directly on the zfs filesystem, I get the following results:
RandomWrite-8k: 0.8M/s SingleStreamWriteDirect1m: 50M/s MultiStreamWrite1m: 51M/s MultiStreamWriteDirect1m: 50M/s Pretty consistent and lovely. The 50M/s rate sounds pretty reasonable, while the random 0.8M/s is a bit too low ? All in all, things look ok to me though here The second step, is to create a 100G zvol, format it with UFS, then bench that under same conditions. Note that this zvol lives on the exact same zpool used previously. I get the following: RandomWrite-8k: 0.9M/s SingleStreamWriteDirect1m: 5.8M/s (??) MultiStreamWrite1m: 33M/s MultiStreamWriteDirect1m: 11M/s Obviously, there's a major hit. Can someone please shed some light as to why this is happening ? If more info is required, I'd be happy to test some more ... This is all running on osol 2008.11 release. Note: I know ZFS autodisables disk-caches when running on partitions (is that slices, or fdisk partitions?!) Could this be causing what I'm seeing ? Thanks for the help Regards
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