Re: Hard Drive Cache Size and XFS Performance

[Michael Loftis <mloftis@xxxxxxxxx>]

on an IDE system especially any and every application benefits HUGELY from 
caching on the drives.   in IDE you can only have one active command on the 
bus at a time.  so the drive has to retire that command before a new one 
can be issued.  in the case of writes this means we can burst writes to the 
drive at the bus speed up tot he size of the cache.  in the case of reads 
the drive can not only read what we asked for, but try to predict what we 
may want next and read that too so then that can come straight out of cache 
without being asked for from the drive and waiting for it to take huge 
amounts of time for the sectors to fly back under the read heads.

with SCSI you benefit atleast as much, and moreso.  if you use tagged 
command queues (multiple active commands per device) the device may be able 
to reorder the execution of the commands  to allow it to fulfill them all 
in a much shorter period of time by perhaps seeking less or waiting less 
for the platters to rotate.  SCSI also has the advantage of multiple active 
commands on the bus so that each target on the bus can have a single 
command ready and going,e ven without tagged command queues.

--On Wednesday, June 30, 2004 08:51 +0800 Federico Sevilla III 
<jijo@xxxxxxxxxxx> wrote:

> Hi everyone,
>
> Please pardon this very basic question.
>
> For single-hard-drive IDE systems with write cache disabled, how
> significantly does a hard drive's cache size affect the performance of
> XFS, all other factors being equal?
>
> We're evaluating hard drives and are comparing two identical Seagate
> 7200RPM drives, the only differences between them being the cache size
> (2MB vs 8MB) and price. Does XFS benefit from a modern hard drive's use
> of its internal cache read-ahead only (since write caching is disabled)?
>
> Thank you very much. :)
>
>  --> Jijo
>
> --
> Federico Sevilla III : jijo.free.net.ph : When we speak of free software
> GNU/Linux Specialist : GnuPG 0x93B746BE : we refer to freedom, not price.



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