Jason Booth <[EMAIL PROTECTED]> posted [EMAIL PROTECTED], excerpted below, on Sun, 22 Oct 2006 11:15:22 -0600:
> On Sunday 22 October 2006 06:16, Richard Freeman wrote: >> I'd just make SWAPDEVICE and LOOPDEV command-line parameters and then >> call the script 4 times. > or drop a for loop into it... > > I don't know much about raid, but if it's treated in /dev as a single device, > you may just be able to replace it and go. The neat thing about swap is that the kernel stripes it on its own -- no raid drivers needed. You just mount the raid swap partitions and set all the ones you want striped to the same priority (I use pri=1), and the kernel will do the rest on its own. If they are all the same size, great, if not, it'll stripe them until the smallest one is gone then it'll stripe the remainder, again all automatically. (Striping means it writes a few bytes, maybe the standard half-kb block tho in the case of swap tho I'm not sure, to the first device, then the next block to the second, the third block to the third, etc. Because bus speed is far faster than physical disk write speed, with four disks by the time you've sent the data to the fourth one, the first is pretty much done actually writing it to disk and ready for more again, so the data is written out and read in at bus speed rather than at bus speed until the cache on the drive fills up or empties, then at drive speed. The caveat with pure striping, aka raid-0, is that while it's much faster, it's not redundant at all, the "r" in "raid" isn't! Thus if one disk goes out, you lost what amounts to everything, tho of course a good data recovery place can still recover say 3 out of every 4 blocks if it was a four-way stripe. However, this isn't a problem as long as you don't need five-nines uptime or the like -- if you want a bad drive to crash the system anyway, so you know about it and can recover the non-raid-0 non-swap data on the other drives due to the redundancy of the other raid formats.) > May be overly paranoid, but writing encrypted data multiple times could help > someone to guess what certain file is and make an attack on the encryption > easier. I use ext2 for my encrypted loops so there's no journal as well. > Although the power fails sometimes, and can be a pain to fsck, i haven't lost > anything yet. If one were using a non-striped raid, say raid-1 (mirrored), or raid-6 (striped minus two, which are parity, so a 4-way is 2-way striped plus two parity, raid-6 allows you to lose any two of the drives), the data would be redundant, but not in pure striped. A redundant raid form swap might be used where uptime is critical and hot-swap drives are used, so the system could continue running after a drive crashed, while it was hot-swapped out. However, that's the big costly operation way of doing things, not a hobbyist's way of doing things unless you are Mark Shuttleworth or something, and going down to replace the drive is expected here anyway, after which the swap could be reconfigured, so no big deal. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- [email protected] mailing list
