On Wed, Feb 01, 2012 at 12:21:17PM -0600, D. Dante Lorenso wrote: >> >Gluster does give you the option of a "distributed replicated" volume, so >> >you can get both the "RAID 0" and "RAID 1" functionality. >> >> If you have 8 drives connected to a single machine, how do you >> introduce those drives to Gluster? I was thinking I'd combine them >> into a single volume using RAID 0 and mount that volume on a box and >> turn it into a brick. Otherwise you have to add 8 separate bricks, >> right? That's not better is it? >I'm in the process of building a pair of test systems (in my case 12 disks >per server), and haven't quite got to building the Gluster layer, but yes 8 >separate filesystems and 8 separate bricks per server is what I'm suggesting >you consider. > >Then you create a distributed replicated volume using 16 bricks across 2 >servers, added in the correct order so that they pair up and down >(serverA:brick1 serverB:brick1 serverA:brick2 serverB:brick2 etc) - or >across 4 servers or however many you're building. > >The advantage is that if you lose one disk, 7/8 of the data is still usable >on both disks, and 1/8 is still available on one disk. If you lose a second >disk, there is a 1 in 15 chance that it's the mirror of the other failed >one, but a 14 in 15 chance that you won't lose any data. Furthermore, >replacing the failed disk will only have to synchronise (heal) one disk >worth of data. > >Now, if you decide to make RAID0 sets instead, then losing one disk will >destroy the whole filesystem. If you lose any disk in the second server you >will have lost everything. And when you replace the one failed disk, you >will need to make a new filesystem across the whole RAID0 array and resync >all 8 disks worth of data. > >I think it only makes sense to build an array brick if you are using RAID1 >or higher. RAID1 or RAID10 is fast but presumably you don't want to store 4 >copies of your data, 2 on each server. The write performance of RAID5 and >RAID6 is terrible. An expensive RAID card with battery-backed write-through >cache will make it slightly less terrible, but still terrible. > >Regards, > >Brian. I would like to second Brian's suggestions. I have almost exactly this setup and it has worked perfectly for well over a year. The added benefit is that you get exactly 50% of the total storage. If you distribute across RAID5/6 arrays you get significantly less than that (i.e. RAID5 costs you 1 disk and RAID6 costs you two disks for each array). Larry Bates vitalEsafe, Inc.
