>Main conditions: > - working like stripe sets, so unit failures will not cause data loss (1 or two server failures are allowed) Gluster replica or dispersed volumes can tolerate that > - scalable, and therefore > - can be extended with one (or maybe two) server at a time (due to low budget) In order to be safe you need 'replica 3' or a disperse volumes. In both cases extending by 1 brick (brick is not equal to node) is not possible in most cases. For example in 'replica 3' you need to add 3 more bricks (brick is a combination of 'server + directory' and it is recommended to be on separate systems or it's a potential single point of failure). Dispersed volumes also need to be extended in numbers of <disperse count>, so if you have 4+2 (4 bricks , 2 are the maximum you can loose without dataloss ) - you need to add another 6 bricks to extend. > - cheap nodes (with 1-2GB of RAM) able to handle the task (like Rpi, >Odroid XU4 or even HP T610) You need a little bit more ram for daily usage and most probably more cores as healing of data in replica is demanding (dispersed volumes are like raid's parity and require some cpu). >As I read a lot about GlusterFS, I recetly concluded that this might also >not be possible with this FS. >At the beginning I thoug! ht, that I create 2+2 disperse volume (for >optimal sector size) that I can later extend to 4+2, even later 6+2 and >continue.... Actually a 2+2 disperse volume will be extended with another 4 disks and will become a 2 * (2+2) , so you will have 2 subvolumes consisting of 2+2 and the algorithm will distribute the data to any of the 2 subvolumes. >Now the question: Can I achieve this with GlusterFS? How? What >configuration I must choose? The idea with the ITX boards is not so bad. You can get 2 small systems and create your erasure coding. So you will have something like this: ITX1:/gluster_bricks/HDD1/brick ITX1:/gluster_bricks/HDD2/brick ITX1:/gluster_bricks/HDD3/brick ITX2:/gluster_bricks/HDD1/brick ITX2:/gluster_bricks/HDD2/brick ITX2:/gluster_bricks/HDD3/brick Then when you create your dispersed volume you should take 3 bricks from ITX1 and 2 from ITX2 (4+2) .Once the volume is created you can expand it with another set of disks . In theory, failure of a system should be tolerable. Yet, I would prefer the 'replica 3 arbiter 1' approach as it doesn't take so much space and extending will require only 2 data disks . Have you thought about 'replica 3 arbiter 1' types of volumes ? Of course you can build software/hardware raid and manage the disks underneath without problems, but every time you change the raid shape you will need to wipe the fs and 'reset-brick'. Best Regards, Strahil Nikolov ________ Community Meeting Calendar: Schedule - Every 2nd and 4th Tuesday at 14:30 IST / 09:00 UTC Bridge: https://bluejeans.com/441850968 Gluster-users mailing list Gluster-users@xxxxxxxxxxx https://lists.gluster.org/mailman/listinfo/gluster-users
