Re: weird throughput on write to SATA disk

[Grant Grundler]

On Tue, Oct 14, 2008 at 2:14 AM, kenneth johansson <ken@xxxxxxxxx> wrote:
...
> All my numbers comes from using 1MB blocks. but I'm not using dd.
> After removing the logic that actually put some data into the buffers I
> do get about 105 MB/sec using O_DIRECT.

Ok. Good.

> I'm doing a full disk write now to get a reference plot.

See http://hdperf.sourceforge.net/  and http://nathan.laredo.name/hdperf/
Simple tool to (relatively) quickly measure the perf across the disk platter.

> Not using O_DIRECT should be almost identical.

*should* - but there are known problems with writeback.
Some of them are described nicely by Dave Chinner as "Random Thought #3":
    http://iou.parisc-linux.org/lsf2008/linux_storage_scalability-Dave_Chinner.odp

Look for "writeback" for a summary of the discussion:
    http://iou.parisc-linux.org/lsf2008/SUMMARY-Storage.txt

hth,
grant
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