Hi Jeff, > "So I would not use any RAID on the machine, just have 8 independent > disks and mount the 8 disks at eight locations:" > > Then your max file size is limited to the space available in each > disk/brick unless you stripe the data with Gluster. I don't think Don was mentionning RAID 0, so yes, I consider stiping in Gluster instead. It will give more flexibility, at the cost of a little speed. To be more exact, the OP is using RAID 0 then replicate with Gluster. Instead I said he may be better be doing the striping and replication in Gluster. RAID 0 will not bring him much, excet headache when he needs to rebuild a 1TB brick instead of a 125GB one (or if he ever find himself in a situation where he has 2 machines with 4 disks each instead of one machine with 8 disks). > Gluster is a replacement for RAID0,1,5,10 it should layer on top of it > to provide more redundancy or speed. The thing is RAID 0 is not provinding any redundancy, only problems :) Note I did not mention any other RAID level. My plan is RAID 10 bricks, in Gluster replicate/striping. > In distribute/replicate your max file size is your brick size is the > best case scenario. 250GB bricks = 250GB max file size. What if your > brick already has 230GB used? Now you max file size it 20G and you get > a full brick if you use it. Create bigger bricks and you have lowered > your chance of having too big of a file and lowered your risk of getting > a full brick. > > I'm fairly new to gluster so if I'm wrong anyone can feel free to > correct me. The only bad thing about big bricks is it makes it harder > to add more bricks since you want to add bricks of the same size if > possible. You can always decide to have pretty "small" briks, like 250GB, and if you have 1TB available on one machine, you create 4 briks on that machine and let gluster stripe them for you. When your hard disk get 1.5TB, you have 6 briks, and that it. You add overhead, you add fragmentation, but you ease-up your managment; it's all a balance of pro's and cons' :) Bests Olivier > Jeff White > Linux/Unix Systems Engineer > University of Pittsburgh - CSSD > Jaw171 at pitt.edu > > > On 10/05/2011 10:45 PM, Olivier Nicole wrote: > > Hi Don, > > > >> Thanks for your reply. Can you explain what you mean by: > >> > >>> Instead of configuring your 8 disks in RAID 0, I would use JOBD and > >>> let Gluster do the concatenation. That way, when you replace a disk, > >>> you just have 125 GB to self-heal. > > If I am not mistaken, RAID 0 provides no redundancy, it just > > concatenates the 8 125GB disks together so they appear as one big 1TB > > disk. > > > > So I would not use any RAID on the machine, just have 8 independent > > disks and mount the 8 disks at eight locations: > > > > mount /dev/sda1 / > > mount /dev/sdb1 /datab > > mount /dev/sdc1 /datac > > etc. > > > > The in gluster I would have the bricks > > > > server:/data > > server:/datab > > server:/datac > > etc. > > > > If any disk (except the system disk) fails, you can simply fit in a > > new disk and let gluster self-heal. > > > > Even if RAID 0 increases the disk throughput because it does stripping > > (write different blocks to different disks), gluster does the same > > more or less, each new file will end up in a different disk. So the > > trhoughput should be close. > > > > The only disadvantage is that gluster will have some space overhead, > > as it will create a replicate of the directory tree on each disk. > > > > I think that you should only use RAID with gluster when RAID provides > > local redundancy (RAID 1 or above): in that case, when a disk fails, > > gluster will not notice the problem, you swap to a new disk and let > > RAID rebuild the information. > > > > Bests, > > > > Olivier >
