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Adaptec RAID 7805 create mirror?

Posted on 2013-06-05
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Last Modified: 2013-06-10
Hi,

If I am trying to create a RAID 1 mirror with 2 4 TB drives how long should I expect to take?
 They are 4 TB seagate drives SATA.

Thanks,

Ward
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Question by:whorsfall
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by:dlethe
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Before you do that .... are you using an O/S & motherboard that will even let you boot a 4TB disk drive?  Most BIOS's won't let you boot a RAID or physical device > 2 TB.   (If this is not going to be the boot disk then no worries).

As for the time it takes. Simple math ... look at the specs on your HDD and see what the sustained non-cached write speed is in MB/sec, and then do the math by multiplying by  4,000,000  [so if it is 100MB/sec, 4000000/100 = 40000 seconds = 40000/3600 hours]

Reads will be faster than writes so that won't be a factor,
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by:garycase
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As dlethe noted, if this is for a boot disk, you first need to confirm you can even use it.

But if it's just for storage, then there's no problem.

To answer you actual question, creating a RAID-4 mirror on a set of 4TB drives should take in the neighborhood of 10 hours if they're 7200rpm drives; about 12-14 on lower RPM "green" units, depending on the specific model.    The Seagate DM series drives should be in the 12 hour range.    These times can be notably longer if the RAID software does a full verification run after the array is created (nearly double) ... but I don't believe that's the case with the Adaptec controller.
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by:dlethe
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another alternative ... the 7805 does have background init, so you could technically just build & configure the RAID1, wait a minute, then start installing the O/S.  

It will do a full RAID1 init in background while you use the system in foreground.  It could very well end up taking > 24 hours before the RAID is fully initialized, but you could start using the system immediately.

Down side, I/O will be significantly slower, and you have no protection against data loss  until the entire disk has been initialized.  Still, you could use the system immediately after kicking off the init.
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by:noxcho
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With two 2TB drives it took in my case 16 Hours.
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by:garycase
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The actual time depends on a variety of factors -- primarily the controller; the drive's rpm;  and the areal density (clearly new 1TB/platter drives are much faster than the older 500MB/platter units).
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by:whorsfall
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Hi,

Thanks for the responses - if I was creating a raid 5 set instead would it add a third more time - 3 drives instead of 2 that is.

Thanks

Ward
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Then the time it could take for ANY given make/model of drive could vary by well over 300% depending on the controller, block size, firmware, # of disks you already have, and how much cache there is.   There is no rule of thumb that will have enough accuracy.  

Best to contact the manufacturer of the controller and see if they have published such numbers for your config.

RAID1 calculations are easy because it really is simple, none of these things come into play, as you are doing 100% non-cached writes at a rate of X MB/Sec, so that spec is published on the HDD spec sheet.

P.S.  DOn't do RAID5 if you can do RAID6 and your data is valuable.  RAID5 does not protect against data loss in event of a drive failure UNLESS all surviving blocks are readable and parity was correct before the failure.  RAID6 gives you greater safety in form of a 2nd parity drive with minor hit in write performance.  Some RAID6 configs are also faster to read than RAID5.
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