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varying internal SATA speeds Mac Pro 12-core

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Dan Wolfe
varying internal SATA speeds Mac Pro 12-core
on Mar 17, 2011 at 11:58:17 pm

just finished a big project, backed up everything, did a clean system reinstall and am setting up for future projects. all of my internal drives are only about 20% full and I just ran AJA system test on all 5 internal drives and have varying speeds. I ran the test three times on each drive and the speeds were consistent for each drive but varied between drives. all drives identical SATA II. any idea(s) why?

LOWER OPTICAL BAY (SYSTEM): 1TB WD CAVIAR BLACK 116/116 MB/s

BAY 1: 2TB WD CAVIAR BLACK 120/120 MB/s
BAY 2: 2TB WD CAVIAR BLACK 86/86 MB/s
BAY 3: 2TB WD CAVIAR BLACK 90/90 MB/s
BAY 4: 2TB WD CAVIAR BLACK 131/131 MB/s

what could be the cause of the speed differences? I want to RAID 0 two of the drives for my scratch disk, the other two are copy A and copy B of my P2 cards. should I pick matched speed bays for the RAID (BAY 1 & BAY 4?)


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Michael Gissing
Re: varying internal SATA speeds Mac Pro 12-core
on Mar 18, 2011 at 12:36:27 am

Try swapping bays to see if it is drive specific. If it is, then yes, choose the two fastest to RAID for media. Personally, I would RAID 5 the lot and have an external to double backup the cards. That way you have greater speed, security and ability to rebuild if a single drive fails and the P2 media could be on both the RAID and an external. win win win.


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Dan Wolfe
Re: varying internal SATA speeds Mac Pro 12-core
on Mar 18, 2011 at 1:31:17 am

well the speeds are drive specific. swapped Bay 2&4 and now the two drives that sustain 120 MB/s are in Bays 1&2 and will become my software RAID 0 for scratch and Bays 3&4 will be P2A and P2B for backup. weird that four identical drives purchased at the same time have different speeds. quality control? ha...


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Michael Gissing
Re: varying internal SATA speeds Mac Pro 12-core
on Mar 18, 2011 at 1:41:33 am

[Dan Wolfe] " weird that four identical drives purchased at the same time have different speeds. quality control? ha..."

I would expect minor differences, but that is a big difference. If you contact WD they might swap out the slow ones.


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Don Walker
Re: varying internal SATA speeds Mac Pro 12-core
on Mar 18, 2011 at 7:52:34 am

Is there any difference between the way they are formatted? Most specifically are 2 of them journaled and the other 2 un-journaled? Highlight the drive, right or cntl click click on "Get Info" and look at the Format. In theory it should say "Mac OS Extended" not "Mac OS Extended Journaled". Some of the smart people on this forum maintain that journaling the drives causes the drives to be slower. I have never tested that, but my scratch disk are not journaled, my P2 backup drives are.

don walker
texarkana, texas

John 3:16


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Tom Matthies
Re: varying internal SATA speeds Mac Pro 12-core
on Mar 18, 2011 at 7:07:24 pm

Speed will also depend on how full the drives are. Are they all new or do some drives have more data on them than the others?

E=MC2+/-2db


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