On Thu, 29 Jun 2006, Leo Huang wrote:

>> >> OS Clients Result(queries per second) TPS(got from
>> >> iostat)
>> >> FreeBSD6.1 50 516.1 about 2000

>> Seems normal for drives that do write caching.

> I disable the driver write caching as Bjorn Gronvall suggest, the
> result show that the TPS come down to about 200. So I think you and
> Bjorn Gronvall are right. It is the disk write caching make the TPS so
> high.
>> >> Debian3.1 50 49.8 about 200

>> Seems to slow for disks that do write caching. Maybe Debian does something
>> to force the drive to complete it's i/o, or just does a full sync() like
>> someone mentioned Linux doing.

> I use sginfo the find that the disk write caching is also enabled
> default. After the disk write caching is disabled, the TPS also come
> down from 200 to 110. This is really pullze me. Can you give me more
> infomation about it?

How did you disable "driver" write caching? I think both Bjorn and I
meant the _drive_ write caching, and that is what you refer to as "disk"
write caching. Only turn off the caching in the lowest layer (disk ==

I wonder when all drives will have enough fast enough nonvolatile RAM for
write caching to just work.

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