On Fri, Mar 23, 2012 at 10:01 AM, Conrad Wood <[email protected]> wrote:
> on storage: > dd if=/dev/zero of=volume bs=1M : ~ 1,600MByte/s > cp file1 file2 : ~ 300MByte/s (both files on same volume) > > on server > dd if=/dev/zero of=volume bs=1M : ~ 1,100MByte/s > cp file1 file2 : ~ 30MByte/s (both files on same volume) > It's not clear to me whether of=volume is writing to the volume or a file on a file system, i.e., is it of=/dev/vol or of=/mountpoint/file1? To be a fair test against 'cp' you should have 'dd' write to a file, though the performance should be fairly close. Also I can't tell if they are direct/synced writes or not, so I'll assume not (sorry for assuming). Your 'dd' numbers look suspiciously high, like buffered writes to RAM. Whenever you want to test actual write performance with 'dd', not memory or dirty page performance, you need to do oflag=direct: dd if=/dev/zero of=/mnt/point/file oflag=direct bs=1M count=1000 Unless you actually want to test writing dirty pages, and I have seen a kernel bug where flushing dirty pages was slow, but then you should also time a 'sync': time dd if=/dev/zero of=/mnt/point/file bs=1M count=1000 && time sync -Anton
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