On 4/26/07, John Elrick <[EMAIL PROTECTED]> wrote:
Some interesting new information, if anyone can make use of it.
After adding one more machine to the test, we have established that the
described slowdown occurs consistently on Windows XP Home and Pro and on
Windows Vista. The problem appears to be absent on Windows Media Center
(two different machines), and may be absent on Windows 2000.
Acording to this [1]:
<quote>
[...]"In Windows 2000, deferred writes are allowed to accumulate in
cache memory until a threshold value for the number of dirty file
pages in cache is reached. An operating system thread to flush dirty
file pages resident in the cache to disk using efficient bulk I/O
operations is then dispatched.
Using lazy write cache management means that Windows 2000 must be
shut down gracefully. Pulling the plug on the computer abruptly
strands numerous file updates parked temporarily in cache memory,
which is why Windows NT issues that "Please wait while the system
writes unsaved data to the disk" message during shutdown. During an
orderly shutdown of the operating system, all dirty pages in the file
cache are flushed to disk before the signal is sent that it is OK to
power off the machine. This means that important Windows 2000 server
machines should always be connected to an uninterruptible power system
(UPS) to prevent data loss due to dirty file pages that have not yet
been written to disk accumulating in the file cache." [...]
</quote>
So it seems you are half right in relation to Windows 2000 (I supose
that threshold value can be configured by some registry value).
But read the full article, because I would guess much of the info
there also apply to Windows XP and Vista.
Regards,
~Nuno Lucas
[1]
http://www.microsoft.com/technet/prodtechnol/windows2000serv/maintain/optimize/wperfch7.mspx
Executing the example Ruby script with pragma synchronous=OFF shows
nearly identical execution times on all machines.
Write caching is enabled on all machines.
My preliminary hypothesis is that Media Center and Windows 2000 may be
far more aggressive about committing data to disk than XP Home and Pro
and Vista. I am still uncertain what factors or configuration settings
could be affecting the performance.
Thanks,
John Elrick
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