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Smart controllers implement RAID 1+0, or 10. What this means is that each individual drive is mirrored, and then striped. This provides much higher availability than 0+1.
I have tested this and it really works.
This is the difference. Let's assume 8 drives. for simplicity, look at it like this:
1 3 5 7
2 4 6 8
In a RAID 0+1, the odd number drives would be striped first (essentially a RAID 0 with drives 1,3,5,7), and then the stripe set mirrored to the even number drives (another RAID 0 with 2,4,6,8). If you lost drive 3, you would still be OK, but if you lost drive 3 and drive 6, you would be hosed because both RAID 0 mirror sets would be broken.
In RAID 1+0, drives 1-2 are mirrored, 3-4, 5-6, and 7-8, then striped. You can lose any combination - up to 4 drives total, as long as they are both not a mirrored pair. So you could lose 1, 4, 5, and 8 and still be running. But if you lost any of the mirrored pairs (like 1-2, 3-4, 5-6, or 7-8) you would be hosed.
And all of this doesn't matter if you only have 2 drives because there's no striping :-)
Thanks,
Doug
In a RAID 0+1
I have tested this and it really works.
This is the difference. Let's assume 8 drives. for simplicity, look at it like this:
1 3 5 7
2 4 6 8
In a RAID 0+1, the odd number drives would be striped first (essentially a RAID 0 with drives 1,3,5,7), and then the stripe set mirrored to the even number drives (another RAID 0 with 2,4,6,8). If you lost drive 3, you would still be OK, but if you lost drive 3 and drive 6, you would be hosed because both RAID 0 mirror sets would be broken.
In RAID 1+0, drives 1-2 are mirrored, 3-4, 5-6, and 7-8, then striped. You can lose any combination - up to 4 drives total, as long as they are both not a mirrored pair. So you could lose 1, 4, 5, and 8 and still be running. But if you lost any of the mirrored pairs (like 1-2, 3-4, 5-6, or 7-8) you would be hosed.
And all of this doesn't matter if you only have 2 drives because there's no striping :-)
Thanks,
Doug
In a RAID 0+1
I am an HPE employee
I was the one who tested it.
Very simple... set it it up just like I described, and then start pulling drives out while you're doing disk I/O
If you start with 8 drives, you can pull up to 4 and it will still be running - just don't pull any 2 that are a mirrored pair!
Also, if you are going to try different combinations of drive pulls, remember that if you put a drive back, you need to wait until it has been fully rebuilt before pulling it's mirror pair.
Thanks,
Doug
Very simple... set it it up just like I described, and then start pulling drives out while you're doing disk I/O
If you start with 8 drives, you can pull up to 4 and it will still be running - just don't pull any 2 that are a mirrored pair!
Also, if you are going to try different combinations of drive pulls, remember that if you put a drive back, you need to wait until it has been fully rebuilt before pulling it's mirror pair.
Thanks,
Doug
I am an HPE employee
yes you are correct. HP Smart Controllers have always done 1+0, so that's basically all I could test.
In some of our documentation quite a few years back, we incorrectly talked about 0+1 as a feature - back when it first came out, nobody in Marketing really thought it through that there might be a difference. This lead to an internal discussion about what the difference between 0+1 and 1+0 was, and when we got the Smart Controller engineering team involved, they verified that from the very beginning, Smart Controllers have done 1+0. So we tried to change all of the references to 0+1 in our documents, but it's possible that some may have been overlooked.
And there is no option within the ACU for Smart Controllers to select 0+1 - it is always 1+0.
Thanks,
Doug
In some of our documentation quite a few years back, we incorrectly talked about 0+1 as a feature - back when it first came out, nobody in Marketing really thought it through that there might be a difference. This lead to an internal discussion about what the difference between 0+1 and 1+0 was, and when we got the Smart Controller engineering team involved, they verified that from the very beginning, Smart Controllers have done 1+0. So we tried to change all of the references to 0+1 in our documents, but it's possible that some may have been overlooked.
And there is no option within the ACU for Smart Controllers to select 0+1 - it is always 1+0.
Thanks,
Doug
I am an HPE employee