On Mon, May 1, 2017 at 10:42 PM, Pranith Kumar Karampuri < [email protected]> wrote:
> > > On Mon, May 1, 2017 at 10:39 PM, Gandalf Corvotempesta < > [email protected]> wrote: > >> 2017-05-01 18:57 GMT+02:00 Pranith Kumar Karampuri <[email protected]>: >> > Yes this is precisely what all the other SDS with metadata servers kind >> of >> > do. They kind of keep a map of on what all servers a particular >> file/blob is >> > stored in a metadata server. >> >> Not exactly. Other SDS has some servers dedicated to metadata and, >> personally, I don't like that approach. >> >> > GlusterFS doesn't do that. In GlusterFS what >> > bricks need to be replicated is always given and distribute layer on >> top of >> > these replication layer will do the job of distributing and fetching the >> > data. Because replication happens at a brick level and not at a file >> level >> > and distribute happens on top of replication and not at file level. >> There >> > isn't too much metadata that needs to be stored per file. Hence no need >> for >> > separate metadata servers. >> >> And this is great, that's why i'm talking about embedding a sort of >> database >> to be stored on all nodes. no metadata servers, only a mapping between >> files >> and servers. >> >> > If you know path of the file, you can always know where the file is >> stored >> > using pathinfo: >> > Method-2 in the following link: >> > https://gluster.readthedocs.io/en/latest/Troubleshooting/gfid-to-path/ >> > >> > You don't need any db. >> >> For the current gluster yes. >> I'm talking about a different thing. >> >> In a RAID, you have data stored somewhere on the array, with metadata >> defining how this data should >> be wrote or read. obviously, raid metadata must be stored in a fixed >> position, or you won't be able to read >> that. >> >> Something similiar could be added in gluster (i don't know if it would >> be hard): you store a file mapping in a fixed >> position in gluster, then all gluster clients will be able to know >> where a file is by looking at this "metadata" stored in >> the fixed position. >> >> Like ".gluster" directory. Gluster is using some "internal" >> directories for internal operations (".shards", ".gluster", ".trash") >> A ".metadata" with file mapping would be hard to add ? >> >> > Basically what you want, if I understood correctly is: >> > If we add a 3rd node with just one disk, the data should automatically >> > arrange itself splitting itself to 3 categories(Assuming replica-2) >> > 1) Files that are present in Node1, Node2 >> > 2) Files that are present in Node2, Node3 >> > 3) Files that are present in Node1, Node3 >> > >> > As you can see we arrived at a contradiction where all the nodes should >> have >> > at least 2 bricks but there is only 1 disk. Hence the contradiction. We >> > can't do what you are asking without brick splitting. i.e. we need to >> split >> > the disk into 2 bricks. >> >> I don't think so. >> Let's assume a replica 2. >> >> S1B1 + S2B1 >> >> 1TB each, thus 1TB available (2TB/2) >> >> Adding a third 1TB disks should increase available space to 1.5TB (3TB/2) >> > > I agree it should. Question is how? What will be the resulting brick-map? > I don't see any solution that we can do without at least 2 bricks on each of the 3 servers. > > > -- > Pranith > -- Pranith
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