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Hitachi Desktar drives in Dell RAID

I have a client that setup a RAID 10 with two WDC Enterprise grade 1TB hard drives and two Hitachi Deskstar 1TB drives - HDS721010CLA332

I know the Hitatchi Deskstar are desktop drives, not server drives. I've had problems in the past in using non-enterprise grade drives in hardware RAIDs.

Is there a particular problem with the above setup or will it work just fine?

Thanks, Jonathan
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Frosty555Commented:
You need to use enterprise grade drives when it's in an enterprise RAID setup. In certain circumstances it's even more restrictive - you have to use the *specific* disks which are vendor-approved, and normally sold by the vendor directly.

Among other things, the main issue with desktop drives is the amount of time they will spend in a deep recovery cycle. If it spends longer than the RAID controller is expecting than it might mistakenly think the disk is nonfunctional and take it out of the RAID array, unnecessarily putting it in a degraded state. If this happens more than once you can lose the entire array.

You don't get this issue on the cheapo implementation of RAID on some consumer motherboards because they are intentionally configured to  avoid this situation, but Dell / IBM / Lenovo servers with vendor-specific RAID cards expect the correct disks.

If you do not use approved disks, you risk data loss. It *is* important.
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DavidPresidentCommented:
Not all RAID controllers will work properly with non-enterprise class disks.  The primary reason is sometimes referred to TLER, which is fancy way of saying the timing for error recovery.

Specifically a controller might only wait 6 seconds for a disk to not respond before it thinks the drive failed. Enterprise disks usually either give up on an unreadable block after 2-3 secs.

But desktop drives may go for well over 30 seconds because premise is that they are not in RAID config and this is only copy of the data.  By the time the drive either recovers or gives up , the RAID controller has already marked the disk dead.



So bottom line DO NOT DO THIS.  They will blame you in event of data loss if you bless this.
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DavidPresidentCommented:
Windows native software RAID 0,1,10 WILL work OK with desktop drives. So get rid of the RAID controller and you will be fine.
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BigSchmuhCommented:
Whatever drive's class that you put in a RAID array, you have TWO mandatory features to take care of:
Enabling the ERC/TLER/CCTL error recovery control to avoid the raid controller to drop out a drive at first sector unrecoverable error - please note that NOT all drive models allow that switch -
Checking volumes consistency using the a "background data scrubber" or a synchronous "check consistency" raid controller feature to enhance your rebuilding success ratio at drive failure time
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BigSchmuhCommented:
Enabling the ERC/TLER/CCTL may be done through the HDAT2 utility
See the user manual § "M4.5.1 Error Recovery Control (ERC)" Menu
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DavidPresidentCommented:
Many years ago the HDD manufacturers caught on, and made the TLER settings VOLATILE on desktop class drives..  So you can reprogram it all day log, but the moment you power cycle, it reverts to factory.

So good luck switching that disk from a JBOD controller to reprogram into the RAID controller w/o power cycling the HDD ;)

(Note certainly it is possible that this particular drive is an exception to the rule, but I haven't run into any seagate, wd, or toshiba drives that are 1TB or larger that haven't switched to making this a volatile setting, so caveat emptor)
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BigSchmuhCommented:
Many years ago the HDD manufacturers caught on, and made the TLER settings VOLATILE on desktop class drives..  So you can reprogram it all day log, but the moment you power cycle, it reverts to factory.
@dlethe : do you have any "official" links to assert this ?

The HDAT2 utility user manual clearly asserts that " These settings are unaffected by software (soft) or hardware (COMRESET) reset." ...

Anyway, this is very easy to try :
-Burn a HDAT2 boot CD
-Boot using SATA standard (not AHCI)
-Try enabling the ERC/TLER/CCTL mode on a drive
-power off and unplug the pc
-Display the current mode using HDAT2 menu
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DavidPresidentCommented:
I had the OEM product manual for that drive.  I can confirm the settings ARE volatile

"... These command timers are volatile. The default value is 0. (i.e. disable command time-out)."

As I wrote, the HDD manufacturers figured this out years ago, and I am not aware of ANY disks made since maybe 2009 that still let people do this.
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DavidPresidentCommented:
The link to the manual is still good. Look at page 94 and see for yourself.   For what it is worth, I wrote a program years ago that would let somebody reprogram the HDD on-the-fly on a bootup to do this when it was behind a certain RAID controller for one of the appliance makers who wanted to save a few bucks.

They ended up never deploying this hack, as we felt if the HDD was in a failure scenario, then there was too much risk of data loss.  

http://www.hgst.com/tech/techlib.nsf/techdocs/39C078C9FA890225862576740063F8D1/$file/7K1000C_USA7K2000_1TB_OEMspec_v2.6.pdf
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