On Sun, 17 Feb 2008 14:31:22 +0100 Janek Kozicki <janek_listy@xxxxx> wrote: > Beolach said: (by the date of Sat, 16 Feb 2008 20:58:07 -0700) > > > I'm also interested in hearing people's opinions about LVM / EVMS. > > With LVM it will be possible for you to have several raid5 and > raid6: eg: 5 HHDs (raid6), 5HDDs (raid6) and 4 HDDs (raid5). Here > you would have 14 HDDs and five of them being extra - for > safety/redundancy purposes. > > LVM allows you to "join" several blockdevices and create one huge > partition on top of them. Without LVM you will end up with raid6 on > 14 HDDs thus having only 2 drives used for redundancy. Quite risky > IMHO. > I guess I'm just too reckless a guy. I don't like having "wasted" space, even though I know redundancy is by no means a waste. And part of me keeps thinking that the vast majority of my drives have never failed (although a few have, including one just recently, which is a large part of my motivation for this fileserver). So I was thinking RAID6, possibly w/ a hot spare or 2, would be safe enough. Speaking of hot spares, how well would cheap external USB drives work as hot spares? Is that a pretty silly idea? > It is quite often that a *whole* IO controller dies and takes all 4 > drives with it. So when you connect your drives, always make sure > that you are totally safe if any of your IO conrollers dies (taking > down 4 HDDs with it). With 5 redundant discs this may be possible to > solve. Of course when you replace the controller the discs are up > again, and only need to resync (which is done automatically). > That sounds scary. Does a controller failure often cause data loss on the disks? My understanding was that one of the advantages of Linux's SW RAID was that if a controller failed you could swap in another controller, not even the same model or brand, and Linux would reassemble the RAID. But if a controller failure typically takes all the data w/ it, then the portability isn't as awesome an advantage. Is your last sentence about replacing the controller applicable to most controller failures, or just w/ more redundant discs? In my situation downtime is only mildly annoying, data loss would be much worse. > LVM can be grown on-line (without rebooting the computer) to "join" > new block devices. And after that you only `resize2fs /dev/...` and > your partition is bigger. Also in such configuration I suggest you > to use ext3 fs, because no other fs (XFS, JFS, whatever) had that > much testing than ext* filesystems had. > > Plain RAID5 & RAID6 are also capable of growing on-line, although I expect it's a much more complex & time-consuming process than LVM. I had been planning on using XFS, but I could rethink that. Have there been many horror stories about XFS? > Question to other people here - what is the maximum partition size > that ext3 can handle, am I correct it 4 TB ? > > And to go above 4 TB we need to use ext4dev, right? > I thought it depended on CPU architecture & kernel version, w/ recent kernels on 64-bit archs being capable of 32 TiB. If it is only 4 TiB, I would go w/ XFS. > oh, right - Sevrin Robstad has a good idea to solve your problem - > create raid6 with one missing member. And add this member, when you > have it, next year or such. > I thought I read that would involve a huge performance hit, since then everything would require parity calculations. Or would that just be w/ 2 missing drives? Thanks, Conway S. Smith - 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
