To create a RAID 0+1 metadevice, one creates two striped metadevices and then one creates a mirror of these metadevices; this is standard practice with DiskSuite.
Creating a RAID 1+0 device requires creating multiple mirrors of disk partition pairs, then striping together the mirror metadevices. The problem is that DiskSuite does not allow the striping of metadevices. Members of a striped metadevice must be physical disk slices, hence RAID 1+0 appears not to be possible with DiskSuite.
However, things are not always as they appear.
If the RAID 0+1 metadevice is created such that the number of columns in each of the mirrored stripes is the same, and the sizes of the physical disk slices in each column is the same, DiskSuite will internally convert that metadevice to a RAID 1+0 device. However, no difference in its outward appearance (for example, using the metastat command) will occur.
As an example, give you what looks to be a RAID 0+1 metadevice:
Code:
d0: Mirror
Submirror 0: d10
State: Okay
Submirror 1: d20
State: Okay
Pass: 1
Read option: roundrobin (default)
Write option: parallel (default)
Size: 7058880 blocks
d10: Submirror of d0
State: Okay
Size: 7058880 blocks
Stripe 0: (interlace: 32 blocks)
Device Start Block Dbase State Reloc Hot Spare
c1t0d0s0 0 No Okay Yes
c1t1d0s0 0 No Okay Yes
c1t2d0s0 0 No Okay Yes
d20: Submirror of d0
State: Okay
Size: 7058880 blocks
Stripe 0: (interlace: 32 blocks)
Device Start Block Dbase State Reloc Hot Spare
c2t0d0s0 0 No Okay Yes
c2t1d0s0 0 No Okay Yes
c2t2d0s0 0 No Okay Yes
However, since DiskSuite treats this device as a RAID 1+0, non-corresponding disks in each submirror CAN fail without any resulting data loss. To illustrate this point, if the disks c1t0d0, c2t1d0, and c1t2d0 were all to fail, the data would still be accessible, despite the fact that all the metadevices are in a "Needs maintenance" state:
Code:
d0: Mirror
Submirror 0: d10
State: Needs maintenance
Submirror 1: d20
State: Needs maintenance
Pass: 1
Read option: roundrobin (default)
Write option: parallel (default)
Size: 7058880 blocks
d10: Submirror of d0
State: Needs maintenance
Size: 7058880 blocks
Stripe 0: (interlace: 32 blocks)
Device Start Block Dbase State Reloc Hot Spare
c1t0d0s0 0 No Maintenance Yes
c1t1d0s0 0 No Okay Yes
c1t2d0s0 0 No Maintenance Yes
d20: Submirror of d0
State: Needs maintenance
Size: 7058880 blocks
Stripe 0: (interlace: 32 blocks)
Device Start Block Dbase State Reloc Hot Spare
c2t0d0s0 0 No Okay Yes
c2t1d0s0 0 No Maintenance Yes
c2t2d0s0 0 No Okay Yes
When replacing these disks, only the disk being replaced will need to be re-synchronized. Again, that is because this metadevice is being treated by DiskSuite as a RAID 1+0 device.
If corresponding disks in each submirror were to fail (such as c1t0d0s0 and c2t0d0s0), data loss would occur. as usual on a raid 1+0, it's not really saver, but it should be faster.... when you think about it, you are just working with luck, based on the probabilistic theory. the idea is that it is not presumably to lose 2 disks of the same pair, in theory. at the end of the day, only one disk should/may fail to provide a redundant lun, everything else is just a game, but think about Murphy's law:
Quote:
* If there's more than one way to do a job, and one of those ways will result in disaster, then somebody will do it that way
* Anything that can go wrong will go wrong
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so it's a great idea to improve the performance, but not to increase the availability
greetings PRESSY
