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SAS vs. Zero Striped Array. Which is faster?

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February 22, 2009 3:33:02 PM

I have been reading about and am intrigued by SAS (Serial Attached SCSI) as far as speed goes.

http://en.wikipedia.org/wiki/Serial_Attached_SCSI

The drives are relatively small in capacity but spin at either 10,000 RPMs or 15,000 RPMs.

This might require an actual benchmark test, but which is faster: a Zero Striped Array or an SAS drive?

The cards that offer RAID ability and SAS ability are expensive -- $600-$800!

I'm thinking of getting a, say 300GB SAS drive, and keeping only my operating system on it (Mac OS X on the next release of a new Mac Pro -- which I now understand may be delayed as it is tied up in court over a suit between Intel and nVIDIA over "Nehalem"). :( 

Everything else I'll keep on another drive.

I understand the operating system uses free disk space for a (I don't know the correct terminology -- "scratch disk"?)

But if I have 8GB RAM wouldn't the entire operating system load into RAM leaving nothing unread on the hard drive?

What then does the OS use free hard drive space for?

Any help is appreciated,

defender
February 23, 2009 9:37:20 PM

assuming your "Zero Striped Array" means raid 0 ( which can be done with all modern hard drive interface types(scsi/sas/ata/sata/sata2.....) heck you can stripe floppies if your bored enough http://ohlssonvox.8k.com/fdd_raid.htm

unless you know your going to be running seek heavy apps ( high traffic web servers/database servers) stick with sata. take the 400+ bux you save and get 3x1.5tb in raid 0 happiness for storage .
if you really want some speed for your os drive go solid state. faster seek times, less power consumption, no noise.

as for speed:
3x7200rpm 1tb sata2 drives will blow away a 300gb sas drive in everything but seek time and costs about the same ( not including the sas controller)
a higher end ( SLC) solid state disk will outperform a 300Gb sas drive without the need for a controller ( but the drive costs more)

either way if your just doing this for your os drive all you'll do is shave a couple of seconds off your boot times.
putting your photoshop temp files or video's your editing or .... where speed is essential on a faster drive will help more.
isolating disk io across 2 cheap sata drives will often buy you better performance than using 1 faster drive.


Quote:
I understand the operating system uses free disk space for a (I don't know the correct terminology -- "scratch disk"?)

But if I have 8GB RAM wouldn't the entire operating system load into RAM leaving nothing unread on the hard drive?

What then does the OS use free hard drive space for?


your os will offload what memory it can to swap space as it feels it needs it. in windows this is almost always. in osx it will be less frequently. even with 8gb of ram it will offload something. you can disable swapping as long as you KNOW you will never exceed your physical ram. bad things happen if you run out of ram with swapping disabled.



hope that helps
February 24, 2009 1:37:35 AM

Thanks, Ignatowski, for your learned and informative reply.

What you say makes perfect sense.

That's why I need people like you! :bounce: 
!