On Mon, Jul 18, 2016 at 3:55 PM, Krutika Dhananjay <kdhananj@xxxxxxxxxx> wrote:
i) Even for a 4TB disk with the smallest possible shard size of 4MB, there will only be a max of 1048576 entriesHere 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:Hi,The suggestion you gave was in fact considered at the time of writing shard translator.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?-KrutikaOn Mon, Jul 18, 2016 at 2:43 PM, Gandalf Corvotempesta <gandalf.corvotempesta@xxxxxxxxx> wrote:2016-07-18 9:53 GMT+02:00 Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>:
> 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.
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