On Mon, May 1, 2017 at 11:20 PM, Shyam <srangana at redhat.com> wrote:
> On 05/01/2017 01:13 PM, Pranith Kumar Karampuri wrote:
>
>>
>>
>> On Mon, May 1, 2017 at 10:42 PM, Pranith Kumar Karampuri
>> <pkarampu at redhat.com <mailto:pkarampu at redhat.com>>
wrote:
>>
>>
>>
>> On Mon, May 1, 2017 at 10:39 PM, Gandalf Corvotempesta
>> <gandalf.corvotempesta at gmail.com
>> <mailto:gandalf.corvotempesta at gmail.com>> wrote:
>>
>> 2017-05-01 18:57 GMT+02:00 Pranith Kumar Karampuri
>> <pkarampu at redhat.com <mailto:pkarampu at
redhat.com>>:
>>
>> > 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/gfi
>> d-to-path/
>> <https://gluster.readthedocs.io/en/latest/Troubleshooting/gf
>> id-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.
>>
>
> Splitting the bricks need not be a post factum decision, we can start with
> larger brick counts, on a given node/disk count, and hence spread these
> bricks to newer nodes/bricks as they are added.
>
Let's say we have 1 disk, we format it with say XFS and that becomes a
brick at the moment. Just curious, what will be the relationship between
brick to disk in this case(If we leave out LVM for this example)?
> If I understand the ceph PG count, it works on a similar notion, till the
> cluster grows beyond the initial PG count (set for the pool) at which point
> there is a lot more data movement (as the pg count has to be increased, and
> hence existing PGs need to be further partitioned) . (just using ceph as an
> example, a similar approach exists for openstack swift with their partition
> power settings).
>
>
>> 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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>> Gluster-users at gluster.org
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>>
>>
--
Pranith
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