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Re: [K12OSN] Are fast disks really that important and why?



How close is SATA2 ncq to the scsi queuing?

On 01/06/07, Sudev Barar <sbarar gmail com> wrote:
On 01/06/07, Paul VanGundy <Paul Vangundy webex com> wrote:
> There's definitely a better way to read disk I/O. Try using 'iostat -k
> 2' and watch as every two seconds you get a read of your disk I/O as
> well as what your cpu utilization is. Pay attention to %iowait as you
> look at it also.
>

Run:
#hdparm -tT /dev/sda (for scsi and sata)
#hdparm -tT /dev/hsa (for PATA ide)

I find the figures returned for cached and buffered disk reads very
much in line with my fast/slow experience in running a LTSP network
with 35 clients. Money allowing I would always go for raid1 scsi. With
cost of one disk and controller already in place one more disk does
not take that much extra.

As already explained the scsi drives requeue or do parallel queuing to
prioritise near by data to the head location resulting in faster user
experience. In PATA/SATA queue is processed one by one resulting in
large head moments where head may have to travel back and forth as
queue are not processed in parallel. This is my understanding till
now.

However newer sata's are good and i would say if money is constrain
then go for raid1 sata's. Why raid1? Avoid the misery of disk going
bad on you. It is worth it.

HTH
--
Regards,
Sudev Barar

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