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RAID 5 System Hard drive size problems.

Posted on 2006-11-06
Medium Priority
Last Modified: 2010-04-03
Hiya all,

Im having some slight issues with a RAID 5 system.

ive got 3 hardrives, all of them Hitachi 72.8 Gb running on a RAID 5, now one of them went down the other day. No problem i thought as ive got another 3 spare for just an emergency.

So i grab another brand new, unopened, HP Nec 72.8 Gb Hd, pop it in the server and prepare to select rebuild.

But then when i try the software gives me an error saying the HD isnt the same size, ie 72 and reports it as a 69Gb in the software. Whereas the current Hitachi 72 ones report theyre at 70 Gb.

i know theres always some size loss depending on HD size but this is stopping me from rebuilding my RAID 5 system when i know that the HD sizes are identical.

Does anyone know a way around this if any? I know if i put a 147 Gb HD in there it'll rebuild fine.

Question by:shellit
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Expert Comment

ID: 17881233
check the firmware of the drives are they identical ?

Author Comment

ID: 17881313
Do i still need to check the firmware even if they are differnet make drives?

The original ones that are in are Hitachi 72 Gb, and ive replaced one of them with a HP 72 Gb.

Would the firmware be the same on them seeing as theyre seprate makes?


Expert Comment

ID: 17881337
ok then no need....

Have you checked if there are any knowledge base on this problem. ?
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Author Comment

ID: 17881363
No i havent, ive never come across this before and ot be fair this is usually my first stop rather than trawling through the base articles.

Do you mean search on the HP site? Or maybe the server make site?

Accepted Solution

cooledit earned 252 total points
ID: 17881371

Expert Comment

ID: 17881377
Both Dell and HP sold these drives ...
LVL 69

Assisted Solution

Callandor earned 248 total points
ID: 17881400
Your problem is that different manufacturers don't use the exact same number when designating the capacity of a drive.  You need a drive that is at least as large as the other drives; it can't rebuild with what it thinks is a smaller drive.  This is the reason you should use the same manufacturer in RAID arrays - identical size, identical performance.

Author Comment

ID: 17881692
I know thats normally the case, but i was also told that as long as theyre the same size then it should work, also our supplier had trouble locating the same drives we purchased off the three years ago =(

I can always return the HDs and get other ones, i just wondered if there was an easier way, this may not be the case =(

Expert Comment

ID: 17882813
As Callandor indicated, this is a difference in how different manufactures will report the size of the drive.  Regardless of what "size" the drive is supposed to be, internally, one manufacturer will report it to the system as maybe 69.9Gb, the next manufacturer may report as similar driver as 69.7Gb. These slight differences will cause the drive to be rejected by Raid Bios if it is smaller than the smallest drive in the current array.
In addition, it is always best to use the exact same drive manufacture, model and version for all array members.
LVL 30

Expert Comment

ID: 17882930
I would set up the new drive and Fdisk it and look for a hidden partition.

A lot of drives come configured with diag partition pre installed.
LVL 56

Expert Comment

ID: 17883475
It's a common problem, some RAID controllers reserve a few hundred MB in case a replacement disk is fractionally smaller but by the looks of it yours didn't. Only way around it is to backup, build a new array (will be slightly smaller due to slightly smaller disk) and restore. Or as you say put a 147GB disk in and wasting half of it. Even a new disk from the same manufacturer isn't guaranteed to be exactly the same size as the current working two.

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