On Mon, Jul 18, 2016 at 3:55 PM, Krutika Dhananjay <kdhan...@redhat.com> wrote:
> Hi, > > The suggestion you gave was in fact considered at the time of writing > shard translator. > Here are some of the considerations for sticking with a single directory > as opposed to a two-tier classification of shards based on the initial > chars of the uuid string: > i) Even for a 4TB disk with the smallest possible shard size of 4MB, there > will only be a max of 1048576 entries > under /.shard in the worst case - a number far less than the max number > of inodes that are supported by most backend file systems. > > ii) Entry self-heal for a single directory even with the simplest case of > 1 entry deleted/created while a replica is down required crawling the whole > sub-directory tree, figuring which entry is present/absent between src and > sink and then healing it to the sink. With granular entry self-heal [1], we > no longer have to live under this limitation. > > iii) Resolving shards from the original file name as given by the > application to the corresponding shard within a single directory (/.shard > in the existing case) would mean, looking up the parent dir /.shard first > followed by lookup on the actual shard that is to be operated on. But > having a two-tier sub-directory structure means that we not only have to > resolve (or look-up) /.shard first, but also the directories '/.shard/d2', > '/.shard/d2/18', and '/.shard/d2/18/d218cd1c-4bd9-40d7-9810-86b3f7932509' > before finally looking up the shard, which is a lot of network operations. > Yes, these are all one-time operations and the results can be cached in the > inode table, but still on account of having to have dynamic gfids (as > opposed to just /.shard, which has a fixed gfid - > be318638-e8a0-4c6d-977d-7a937aa84806), it is trivial to resolve the name of > the shard to gfid, or the parent name to parent gfid _even_ in memory. > s/trivial/non-trivial/ in the last sentence above. Oh and [1] - https://github.com/gluster/glusterfs-specs/blob/master/done/GlusterFS%203.8/granular-entry-self-healing.md -Krutika > > > Are you unhappy with the performance? What's your typical VM image size, > shard block size and the capacity of individual bricks? > > -Krutika > > On Mon, Jul 18, 2016 at 2:43 PM, Gandalf Corvotempesta < > gandalf.corvotempe...@gmail.com> wrote: > >> 2016-07-18 9:53 GMT+02:00 Oleksandr Natalenko <oleksa...@natalenko.name>: >> > I'd say, like this: >> > >> > /.shard/d2/18/D218CD1C-4BD9-40D7-9810-86B3F7932509.1 >> >> Yes, something like this. >> I was on mobile when I wrote. Your suggestion is better than mine. >> >> Probably, using a directory for the whole shard is also better and >> keep the directory structure clear: >> >> >> >> /.shard/d2/18/D218CD1C-4BD9-40D7-9810-86B3F7932509/D218CD1C-4BD9-40D7-9810-86B3F7932509.1 >> >> The current shard directory structure doesn't scale at all. >> _______________________________________________ >> Gluster-users mailing list >> Gluster-users@gluster.org >> http://www.gluster.org/mailman/listinfo/gluster-users >> > >
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