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If I use a dual-disk enclosure that employs JBOD, would I be able to at least access and use a second disk in the event that the other fails or otherwise becomes inaccessible?
James
Posted 2013-04-07T19:25:56.993
Reputation: 477
If one disk in a JBOD group fails, are files on other disks inaccessible?
Answers
3
JBOD means no RAID, incuding the 'R' part that means redundancy unless you did this with other means.
JBOD across two disks without RAID is spanning a volume across two physical disks. There is no redundancy (unless your documentation tells you different - both JBOD and RAID can mean different things to different people sometimes). Technologies to do this include Windows "dynamic volumes" and Linux's LVM.
In a spanned volume, if one disk goes down, data on the entire spanned volume, i.e. ALL your data, is at risk.
If you want to be able to access the volume if a disk in it fails you need some type of redundancy and pay for it with disk space, either hardware RAID or a software equivalent.
LawrenceC
Posted 2013-04-07T19:25:56.993
Reputation: 63 487
1JBOD doesn't mean that the disks are combined into a single logical volume. It's short for "just a bunch of disks", meaning that it's just like plugging the drives into a plain non-RAID controller and using them as plain, independent disks. – Wyzard – 2014-03-03T00:47:40.427
@Wyzard: Very true. I imagined a dual-disk enclosure would typically be spanning across disks. I could be wrong. If they aren't spanned, you'll only lose data that's on the one disk. – LawrenceC – 2014-03-03T01:44:02.527
2
I'm a raid guy (0, 1, 5 ) and have never used jbod, but it appears that losing a drive wil be the equivalent of having a volume with lots and lots of unreadable sectors that are unrecoverable. Any data stored entirely on a still-working drive would be recoverable.
Any data stored (even partially) on the failed drive would be lost.
http://forum.wegotserved.com/index.php?/topic/9244-one-disk-in-jbod-array-dies-help/
Brian Adkins
Posted 2013-04-07T19:25:56.993
Reputation: 1 721
2
That depends on where the MFT (or equivalent) was stored. If you lose the MFT, you are pretty much out of luck. You should really consider backups if you plan on using JBOD.
1
Almost always, yes. If one drive fails the others will still be readable. With data arrays including (RAID and JBOD) you should have backup but my guess is that if you're using JBOD it's because you have lots of data and little money so that recommendation won't mean anything to you till you loose your irreplaceable data.
Frank
Posted 2013-04-07T19:25:56.993
Reputation: 11
Be aware that the combined disk's fail rate will be significantly higher. Say the chance of one disk being OK is 0.99 then a 2 disk JBOD will be OK = 0.99 * 0.99 = 0.98. A Five disk JBOD will be 0.99^5 = 0.95. Hence if there was a 1% chance of failure (say during one year for one disk), there will be a 5% chance of failure for a JBOD (5 times the risk). - laurits
– Canadian Luke – 2013-06-15T22:25:18.637