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raid 5 rebuild with same model but different size hard drive

Posted on 2007-08-03
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Last Modified: 2010-05-18
Adabtec 2100S Raid card

One of our hard drives went down which brought our raid down to degraded status.  We ordered a replacement hd of the exact same model.  Well the hard drive is a different revision and has about 280mb less storage space than the original.  When I try to rebuild the drive is gives me a warning stating that the drive is smaller than the current raid are you sure you want to proceed

My questions is...  How likely will the hard drive be successfull if I try to go ahead and put it in the Raid?  Or do i need to get one that is larger than the current hard drives?  A quick response would be greatly appreciated!!!
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Question by:inimicaljords
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by:Christopher McKay
Christopher McKay earned 300 total points
ID: 19626281
You would be much better off to order a larger hard drive as a replacement.
You run the risk of losing data if the RAID gets picky and upset over the difference, as it is smaller, if you use a larger hard drive, it won't care, it will just ignore the excess.

Hope this helps!

:o)

Bartender_1
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by:Lee W, MVP
Lee W, MVP earned 700 total points
ID: 19626318
You cannot use a drive SMALLER than the original drive.  You DO NOT need an identical drive to replace the failed drive.  You CAN use a different model or even a different brand.  Indeed, even the RPM doesn't NEED to be the same.  I WOULD try to match the RPM though, but it really doesn't matter - the drive will perform at the specs of the "worst" drive.
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by:inimicaljords
ID: 19626491
does the MS matter?

This is the hard drive we ordered which is 280mb to small but is the same model as the ones in the unit already but has a different revision number.

36.0GB 4.7MS/10000 (ULTRA 320 68PIN) 8192K 3.5"/LP NEW PULL 1 YEAR WARRANTY THRU US
      
ST336607LW

They are only running at 160 though not 320

would this one work?

36.7GB 5.4MS/10000 (ULTRA 160 80PIN) 4096K 3.5"/LP EMC PULL 1 YEAR WARRANTY THRU US
      
ST336704LC
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by:inimicaljords
ID: 19626501
never mind its 80 pins vs 68 pints, just realized it
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Lee W, MVP earned 700 total points
ID: 19626577
Why are you getting a SCSI hard drive with ONLY a 1 year warranty?  You shouldn't buy one with LESS than a 5 year warranty.

You also need to understand how SCSI works - the ENTIRE BUS runs at what the controller is capable - 10,20,40,80,160,320.  If you have one drive, than you'll have one drive running at the controller's speed (lets say 320).  But even that will fall back to whatever the drive supports.  Now if you have two drives, that 320 is divided by 2 and the performance is 160 per drive (when they are accessed simultaneously.  Have 8 drives, then during simultaneous access, expect 20 MB/per drive.
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by:inimicaljords
ID: 19626634
I am looking for something to replace the seagate ST336607LW.  Need a slightly bigger hard drive though.  I am assuming a 36.7GB would work as long as it has 68 pins, Ultra 320, 10k rpm correct?  


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by:Handy Holder
ID: 19630878
Hmm, Adaptec must have updated their firmware; last time I tried with a slightly smaller drive it tried to rebuild and then complained at the end rather than at the beginning.

I think you can use the current disk but take some precaution first; run a partition migration utility that can shrink the volume under the OS by 1 or 2 GB, then let it rebuild and ignore the warning since there won't be any data where you have no parity. Confirm this with Adaptec though, they might have a whitepaper or knowledgebase article on it. If we had the exact text of the warning it would help find info.
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by:Lee W, MVP
ID: 19631766
Why not play it safe, even plan for the future and just buy a 73 GB drive?
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by:inimicaljords
ID: 19658249
I appreciate everyones input.  I was to scared to try the rebuild on the smaller hard drive so we order a 73GB drive and was able to successfully rebuild it and got it back working!.  Thanks for the advice!!
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Expert Comment

by:JanSchotsmans
ID: 20130219
I personally would scrap the manifacturer of the harddrive you have as a hardware vendor.

They of all people should know that they can't revision SCSI disks which are often used in RAID arrays to be smaller then the original.

I sure hope they didn't make a deal about replacing the disk or giving you your money back.
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Expert Comment

by:snowdog_2112
ID: 24865204
This is CRAP!  I ran into the *same* thing with a different Seagate drive model: ST336752LC.  I had 3 original drives with firmware 0002 - all registered in the RAID BIOS as 34971MB.

One drive failed, so I ordered another ST336752LC, this time I got a newer firmware on the drive and it shows up as only having 34700MB!!!!

So, I'm out my $$, out 200MB, and I *still* can't rebuild the array!!!

What kind of underhanded crap is Seagate pulling with server-class hard drives????

*VERY ANGRY*
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Expert Comment

by:Handy Holder
ID: 24867104
You may be able to increase the size using seatools for DOS, the drive may be OEM'ed to someone who has low level formatted* it to a smaller size than it really is. (not really formatted but set the size parameter to less than maximum). With seatools for DOS I can take your ST336752LC and tell it to report its size as 10GB, you can hardly blame Seagate if someone uses SCSI commands to tell the disk to pretend to be smaller than its full size.
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