-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Les Mikesell Sent: Thursday, May 10, 2007 9:41 AM To: CentOS mailing list Subject: Re: [CentOS] Re: Anaconda doesn't support raid10
Andreas Micklei wrote:
Am Donnerstag, 10. Mai 2007 schrieb Feizhou:
Probably not, but is SATA really much worse then SCSI or
SAS? I did
some testing on a dell PE 2950 of 750GB SATA's vs SAS and
SCSI drives,
and the SATA drives seem to be faster at least at first
glance. I don't
have good numbers from the SCSI tests, but at least for
sequantial, I'm
getting a better speed off the SATAs.
sequential will be better than SCSI due to the packing on
those platters
which make up for the lack in rpm. NCQ should even up the
random ability
of SATA disks versus SCSI drives but that support has only become available lately on Linux and you also need the right
hardware (besides
the right disks).
SAS and SCSI really has it's place when you need random
access with lots of
IOs per second, i.e. Fileserver, Database Server. We
upgraded our Fileserver
(NFS, Samba) from SATA SW Raid to SCSI HW Raid and the
difference is HUGE.
One the old system a single user doing a large file copy
could bring the
system almost to a halt. On the new system you do not even
notice if one user
does a similar operation. However plugging one of the same
SCSI discs into
your average PC will not give you much advantage.
There is also a line of SATA discs that aim for the low-end
server market, the
WD-Raptors. They spin at 10.000 rpm and give much better
random access
performance than normal SATA drives. The price point is
very attractive
compared to SCSI and SAS. Great alternative for a tight budget.
Here is my favorite site for comparing drives. Has nice
background articles
I've always wanted a dollars to dollars comparison instead of comparing single components, and I've always thought that a bunch of RAM could make up for slow disks in a lot of situations. Has anyone done any sort of tests that would confirm whether a typical user would get better performance from spending that several hundred dollars premium for scsi on additional ram instead? Obviously this will depend to a certain extend on the applications and how much having additional cache can help it, but unless you are continuously writing new data, most things can live in cache - especially for machines that run continuously.
RAM will never make up for it cause user's are always accessing files that are just outside of cache in size, especially if you have a lot of files open and if the disks are slow then cache will starve to keep up.
Always strive to get the best quality for the dollar even if quality costs more, because poor performance always makes IT skills look bad.
Better to scale down a project and use quality components then to use lesser quality components and end up with a solution that can't perform.
SATA is good for it's size, data-warehousing, document imaging, etc.
SCSI/SAS is good for it's performance, transactional systems, huge multi-user file access, latency sensitive data.
-Ross
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