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

[Peter Scheie]

Can't find the article, but Wikipedia has some good articles the compare 
SCSI, Serial ATA, Tagged Command Queuing (TCQ, SCSI), and Native Command 
Queuing (NCQ, SATA).  There are also some links to external articles on 
the matters.


Peter Scheie wrote:
> It's getting close to SCSI, but SCSI is still better especially as the 
> number of users (and therefore requests) climbs.  I read an article some 
> months ago that explained in detail the evolution of SATA, how compares 
> to SCSI, how SATA2 may be adequate for many (most?) situations, 
> especially when the number of users is smaller, and how in larger 
> multi-user settings SCSI is still best the way to go.  I'll see if I can 
> dig that up.
> 
> Petre
> 
> Krsnendu dasa wrote:
>> How close is SATA2 ncq to the scsi queuing?
>>
>> On 01/06/07, Sudev Barar <sbarar at gmail.com> wrote:
>>> On 01/06/07, Paul VanGundy <Paul.Vangundy at 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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>>
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