On Tuesday September 20, sgunderson@xxxxxxxxxxx wrote: > (Please Cc me on any replies, I'm not subscribed) ofcourse... > > Hi, > > Attached is a patch (against 2.6.12) for adding online RAID-5 resize > capabilities to Linux' RAID code. Wow! Thanks for this. It's been something that I wanted to be done for some time, but it hasn't got even close to the top of my todo list. > > - It's RAID-5 only; I don't really use RAID-0, and RAID-6 would probably be > more complex. I doubt raid6 would be much more difficult. However it is definitely best to get it working well in raid5 first. I'd never thought of doing raid0, but I cannot now think of a good reason not to..... > - It supports only growing, not shrinking. (Not sure if I really care about > fixing this one.) Shrinking certainly adds a lot of complications, and you would have to start at the 'top' and work backwards. Probably not worth the effort, except that people might want to be able to back-out a change... > - It leaks memory; it doesn't properly free up the old stripes etc. at the > end of the resize. (This also makes it impossible to do a grow and then > another grow without stopping and starting the volumes.) I'm sure that can be fixed. > - There is absolutely no crash recovery -- this shouldn't be so hard to do > (just update the superblock every time, with some progress meter, and > restart from that spot in case of a crash), but I have no knowledge of the > on-disk superblock format at all, so some help would be appreciated here. > Also, I'm not really sure what happens if it encounters a bad block during > the restripe. Crash recovery is essential I think. There are some awkward cases, particularly while growing the first few stripes. I'm sure we can work it out together. > - It's quite slow; on my test system with old IDE disks, it achieves about > 1MB/sec. One could probably make a speed/memory tradeoff here, and move > more chunks at a time instead of just one by one; I'm a bit concerned > about the implications of the kernel allocating something like 64MB in one > go, though :-) I doubt speed is a top priority. I'll try to have a read through your code over the next week or so and give you more detailed feedback. Thanks again, NeilBrown - 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
