Caporegime
- Joined
- 20 Oct 2002
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- 78,538
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- Wish i was in a Ramen Shop Counter
I have a Drobo, it says it run something call "Beyond RAID" technology, but in theory it is probably a kind of modified RAID. I know for a fact that it needs 2 HD to work, and when you have 2 HD, it basically runs in RAID 1 - Mirror, and if you have 3 HDs, it runs Parity?
(It can also run with dual disc redudancy setting, this kills the capacity of the NAS itself as it uses a lot of space for back up)
Now….I have been thinking, and to make it easier, this is what I understand. When running 1 Disk fail mode.
In a 2 HDs set up
2 x 2TB = 1.78TB capacity, as it is running mirror.
So if one fails, the other one is fine.
In a 3 HDs set up.
Now if one HD fails, it will start doing things and move data in the 2 HD and run it in Mirror Mode? So in theory, if I have less than 900G of data across 3 discs, even running in 1 Disk fail mode, it can allow up to 2 disc to fail? As if one disk fails in the 3 disks, it should go into RAID 1 mode? That of course providing you have less than 900G (1/3) of the capacity, and I presume this will apply when running 5 Disks.
So, why would anyone run with dual disk failure unless you get 2 disks fails in a short space amount of time, before the NAS can move the data around (which can take up to 12 to 24 hours ) ?
(It can also run with dual disc redudancy setting, this kills the capacity of the NAS itself as it uses a lot of space for back up)
Now….I have been thinking, and to make it easier, this is what I understand. When running 1 Disk fail mode.
In a 2 HDs set up
2 x 2TB = 1.78TB capacity, as it is running mirror.
So if one fails, the other one is fine.
In a 3 HDs set up.
Now if one HD fails, it will start doing things and move data in the 2 HD and run it in Mirror Mode? So in theory, if I have less than 900G of data across 3 discs, even running in 1 Disk fail mode, it can allow up to 2 disc to fail? As if one disk fails in the 3 disks, it should go into RAID 1 mode? That of course providing you have less than 900G (1/3) of the capacity, and I presume this will apply when running 5 Disks.
So, why would anyone run with dual disk failure unless you get 2 disks fails in a short space amount of time, before the NAS can move the data around (which can take up to 12 to 24 hours ) ?