Hello fellow RAIDers, I'm looking for some pointers on how I might best configure my modest mdraid array. After some unfortunate hardware failures, it looks like I will not be able to recover my existing array. (This is a minor annoyance, which is why I'm leaning towards starting over instead of spending more time trying to recover.) My basic situation: I have a 16-bay chassis attached to a 3ware 9550 controller. I'm really unhappy with the controller, but am wary of replacing it for various reasons (hard to find PCI-X controllers, very hard to find 16-port PCI-X controllers, cards I've found would need cables replaced as well). And, as we've talked about on list, enterprise-class drives are hard to find as well, at least for a few months, so I need to battle my EARS/EADS drives for at least a little longer. (I do have 5 RE4 drives I can use, and may test some of the Hitachis we've talked about.) My last array was a 10x2TB RAID6 resulting in about 15TB of usable storage; at the time it was ~90% full, but if my snapshots are gone I may have some time where I don't get quite that full. I am looking for the best compromise between maximizing storage, defending against the EADS drives, the potential to recover from multiple drive failures, and being able to swap out the EADS drives quickly once I'm able to get better drives. Easy, right? ;-) So, some options I'm tossing around: -- [ot] LVM or no LVM? I am certainly not well-versed in LVM, but it's certainly possible that LVM helped contribute to not being able to recover the existing filesystem. I am wondering if it is worth the extra overhead (and metadata) to get the benefits of LVM if the odds are slim that I'll have storage I can't integrate into the md RAID arrays. I know that's OT, but... --RAID6, RAID50, RAID5s+LVM, separate RAID5s? RAID6 maximizes storage, but has longer rebuild times; any RAID5 combination makes rebuilds (and reshapes?) faster, but I worry that there's less leeway in an individual RAID5 if there's one with multiple EADS drives. One option I had in mind was to throw as many of my enterprise drives at my more important snapshots, and put the EADS drives all together to snapshot the less important data. So perhaps I could have a RAID6 that included all the RE4 drives, plus two EADS drives, for ~9TB usable, and a RAID5 or RAID6 with four or five drives for the rest. Or I could make two four drive RAID5s, either in a RAID50 or LVM, for ~11TB usable (I would want to find another RE4 or equivalent for this). Are there any appreciable advantages of RAID50 over RAID5s grouped together by LVM or vice-versa? They seem very similar superficially. Can I add a disk and reshape one member of a RAID50 without modifying the other? I don't think the 3ware 9550 supports that. This situation seems like it's the stereotypical use case for LVM, but perhaps a plain RAID50 has advantages that make it preferable. --Finally, the age-old argument: whole disks or partitions? I wonder if this is the mdraid equivalent of emacs vs. vi. :) I used partitions in the last array, but TBH I wasn't all that happy with it, though I couldn't explain why. It could be I'm just used to working with whole disks on RAID controllers. --Any other pointers/advice/gotchas? Thanks for reading--if you've made it this far I probably owe you a beer! --keith -- kkeller@xxxxxxxxxxxxxxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
