I missed an important conclusion from j's data, and that is that single disk raw access gives him 56MB/s, and RAID 0 array gives him 961/46=21MB/s per disk, which comes in at 38% of potential performance. That is in the ballpark of getting 45% of potential performance, as I am seeing with my puny setup of single or dual drives. Of course, I don't expect a complex file system to match raw disk dd performance, but it doesn't compare favourably to common file systems like UFS or ext3, so the question remains, is ZFS overhead normally this big? That would mean that one needs to have at least 4-5 way stripe to generate enough data to saturate gigabit ethernet, compared to 2-3 way stripe on a "lesser" filesystem, a possibly important consideration in SOHO situation.
On 5/14/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
This certainly isn't the case on my machine. $ /usr/bin/time dd if=/test/filebench/largefile2 of=/dev/null bs=128k count=10000 10000+0 records in 10000+0 records out real 1.3 user 0.0 sys 1.2 # /usr/bin/time dd if=/dev/dsk/c0t0d0 of=/dev/null bs=128k count=10000 10000+0 records in 10000+0 records out real 22.3 user 0.0 sys 2.2 This looks like 56 MB/s on the /dev/dsk and 961 MB/s on the pool. My pool is configured into a 46 disk RAID-0 stripe. I'm going to omit the zpool status output for the sake of brevity. > What I am seeing is that ZFS performance for sequential access is > about 45% of raw disk access, while UFS (as well as ext3 on Linux) is > around 70%. For workload consisting mostly of reading large files > sequentially, it would seem then that ZFS is the wrong tool > performance-wise. But, it could be just my setup, so I would > appreciate more data points. This isn't what we've observed in much of our performance testing. It may be a problem with your config, although I'm not an expert on storage configurations. Would you mind providing more details about your controller, disks, and machine setup? -j
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