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Understanding RAID 10 (2+2) or (4+4)
Hi all,
I am new to storage.
I understand what RAID10 (2+2) is (stripped mirror) whereby there are data are striped across 2 groups and each group have a pair of mirror devices (2 disks).
This is how i have understand "2+2"
For RAID10 4+4, is it
- striping across 4 groups, each group still having 2 mirrored devices or
- striping across 2 groups, each group have 4 mirrored devices
- striping across 4 groups, each group have 4 mirrored devices
2 and 3 just doesn't make sense.
q1) How is 1) a 4+4 then ?
q2) why does some people says that raid10 (4+4) has lower reliability then RAID 10 (2+2)
Regards,
Noob
umichklewis
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March 10th, 2016 15:00
Each RAID10 member is a single, mirrored pair, stripped across multiple members (groups, in your parlance). Think of RAID10 as "mirroring [1]" then "striping [0]".
So, RAID10 (2+2) means, I have two pairs of mirrored disks, or a stripe of two pairs (four drives in total). RAID10 (4+4) means I have four pairs of mirrored disks, or a stripe of four pairs (eight drives in total). RAID10 (8+8) means I have eight pairs of mirrored disks (16 drives in total).
People might say that RAID10 4+4 is less reliable than RAID10 2+2, if they're referring to "failure domains". Think of it like this: what's more resilient: one group of four mirrors or two groups of two mirror? With two RAID10 2+2 groups, I can lose any two drives in either group (four total) and still have access to data. With one RAID10 4+4 group, I can only lose one only one drive per mirrored pair and still have access to data. If a RAID10 4+4 group loses both mirrors (two drives) in a pair, you lose access to data.
Let us know if that helps!
Karl