On Tue, Jan 29, 2008 at 01:34:37PM -0600, Moshe Yudkowsky wrote: > > I'm going to convert back to the RAID 1 setup I had before for /boot, 2 > hot and 2 spare across four drives. No, that's wrong: 4 hot makes the > most sense. > > And given that RAID 10 doesn't seem to confer (for me, as far as I can > tell) advantages in speed or reliability -- or the ability to mount just > one surviving disk of a mirrored pair -- over RAID 5, I think I'll > convert back to RAID 5, put in a hot spare, and do regular backups (as > always). Oh, and use reiserfs with data=journal. Hmm, my idea was to use a raid10,f2 4 disk raid for the /root, or a o2 layout. I think it would offer quite some speed advantage over raid5. At least I had on a 4 disk raid5 only a random performance of about 130 MB/s while the raid10 gave 180-200 MB/s. Also sequential read was significantly faster on raid10. I do think I can get about 320 MB/s on the raid10,f2, but I need to have a bigger power supply to support my disks before I can go on testing. The key here is bigger readahead. I only got 150 MB/s for raid5 sequential reads. I think the sequential read could be significant in the boot time, and then for the single user running on the system, namely the system administrator (=me), even under reasonable load. I would be interested if you would experiment with this wrt boot time, for example the difference between /root on a raid5, raid10,f2 and raid10,o2. > Comments back: > > Mr. Tokarev wrote: > > >By the way, on all our systems I use small (256Mb for small-software > >systems, > >sometimes 512M, but 1G should be sufficient) partition for a root > >filesystem > >(/etc, /bin, /sbin, /lib, and /boot), and put it on a raid1 on all... > >... doing [it] > >this way, you always have all the tools necessary to repair a damaged > >system > >even in case your raid didn't start, or you forgot where your root disk is > >etc etc. > > An excellent idea. I was going to put just /boot on the RAID 1, but > there's no reason why I can't add a bit more room and put them all > there. (Because I was having so much fun on the install, I'm using 4GB > that I was going to use for swap space to mount base install and I'm > working from their to build the RAID. Same idea.) If you put more than /boot on the raid1, then you will not get the added performance of raid10 for all your system utilities. I am not sure about redundance, but a raid1 and a raid10 should be equally vulnerable to a 1 disk faliure. If you use a 4 disk raid1 for /root, then of cause you can survive 3 disk crashes. I am not sure that 4 disks in a raid1 for /root give added performance, as grub only sees the /root raid1 as a normal disk, but maybe some kind of remounting makes it get its raid behaviour. > >Also, placing /dev on a tmpfs helps alot to minimize number of writes > >necessary for root fs. I thought of using the noatime mount option for /root. best regards Keld - 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
