> On Wed, Jan 5, 2011 at 4:03 PM, Leslie Rhorer <lrhorer@xxxxxxxxxxx> wrote: > >> 1) The Linux/MySQL stuff is a 3 drive RAID1. (sda/sdb/sdc) > > > > Well, RAID1 certainly offers the most robust solution, especially > > with more than 1 mirror. > > > <SNIP> > > > >> 3) There is a second RAID1 (sda/sdb/sdc) used for backups of the > >> RAID0. The RAID0 is backed up to RAID1 nightly. If the RAID0 fails > >> then I lose 1 day's work. > > > > Well, first of all, unless you meant to say sda1/sdb1/sdc1, etc, > > then this can't be different from the #1 RAID array above. Assuming you > are > > actually using partitions, then I don't really see the value of two > separate > > arrays. Why not just one RAID1 array? > > > > Sorry I wasn't very clear. > > In #1 the RAID1 is my main Linux system on sda3/sdb3/sdc3. > In #3 the RAID1 is purely for backups on /swa6/sdb6/sdc6 and is used > only for the backup of the RAID0 data. It is not normally mounted > except when doing backups. I wanted the extra protection that if > something went wrong with the basic Linux box the backup partition > would not normally be mounted and the data hopefully a bit safer. > > > > Also, I personally would reverse the backup strategy. I would > put > > the Windows VM on the (single) main RAID array and back up the data to a > > single 1T hard drive. > > > > I do this today backing up the existing RAID1 partitions to an > external eSATA 1TB drive. What I meant was, you currently have a 2 disk RAID0. Why not buy a larger disk and move the 2 drives currently tied up in the RAID0 to a 5 disk RAID6 array with no partitions? The function currently provided by the 2nd RAID1 can be taken over by the single drive, and the function of the RAID0 can be taken over by a directory on the main array. This makes better functional use of the space and may provide performance benefits, not to mention being much simpler. I'm a fan of having a separate, small disk for booting. My servers both have a pair of small drives each partitioned into three sections. Each of the partition pairs are in turn assembled into a RAID array for a total of 3 mounts: md1 - a tiny /boot md2 - a small / md3 - swap. > >> OK - the problems I have with this arrangement are: > >> > >> 1) I used the older v0.9 metadata. > > > > This may be necessary if you are booting from the array. The > > limitations of the 0.90 superblock may never impact you. That's a small > > system with only a few drives. > > > >> 2) The RAIDs are assembled by the kernel automatically. I do not use > >> an initrd. (Because I don't know how/newer have) > > > > How is that a problem? An initrd, or lack thereof, won't prevent > > you from disabling the automatic assembly of one or more arrays, unless > once > > again you boot from the array in question. Most modern distros default > to > > using an initrd. What distro are you using? > > > > The machines are Gentoo and an initrd/initramfs is up to the builder. > The new RAID6/superblock-1.2 boot uses one. The RAID1/superblock-0.9 > does not. OK, well, either way, any array can have auto-assembly disabled. If you go with a single RAID6 plus a simple drive, it won't be required, though. > >> 3) I think with 5 disks I could get better performance than I > >> currently get , with similar or better safety using maybe RAID5 or > >> RAID6. > > > > No, RAID1 is as safe as it gets. RAID0 allows for better > > performance, but if you make the RAID0 into your backup solution, the > > performance won't matter much. > > > > If I'm wrong about RAID6 please correct me as this understanding is > why I chose it. > > 1) A 5-drive RAID6 can survive losing 2 disks and still return good data. Yes. > 2) A 5-drive RAID6 reads data as nearly fast as a 3-drive RAID0. Or faster. Right now your 3 drive arrays are RAID1, though, aren't they? RAID6 should read *MUCH* faster than RAID1 > If those two aren't true then my choice of RAID6 doesn't improve my > system as I hoped. > > 3) My current 3-drive RAID1 can lose 2 disks and still return good > data making #1 equivalent to #3 Well, only in terms of survivability and only for the configuration you mention. An N drive RAID1 array can lose N-1 drives. Any RAID6 array can lose 2 drives. > 4) #2 would be faster than my current 2-drive RAID0 and wouldn't have > the risk of a single drive loss. Yes. -- 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
