From: "Venky Shankar" <vshankar@xxxxxxxxxx>
To: "Aravinda" <avishwan@xxxxxxxxxx>
Cc: "Shyam" <srangana@xxxxxxxxxx>, "Krutika Dhananjay" <kdhananj@xxxxxxxxxx>, "Gluster Devel" <gluster-devel@xxxxxxxxxxx>
Sent: Thursday, September 3, 2015 8:29:37 AM
Subject: Re: Gluster Sharding and Geo-replicationOn Wed, Sep 2, 2015 at 11:39 PM, Aravinda <avishwan@xxxxxxxxxx> wrote:
>
> On 09/02/2015 11:13 PM, Shyam wrote:
>>
>> On 09/02/2015 10:47 AM, Krutika Dhananjay wrote:
>>>
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> *From: *"Shyam" <srangana@xxxxxxxxxx>
>>> *To: *"Aravinda" <avishwan@xxxxxxxxxx>, "Gluster Devel"
>>> <gluster-devel@xxxxxxxxxxx>
>>> *Sent: *Wednesday, September 2, 2015 8:09:55 PM
>>> *Subject: *Re: Gluster Sharding and Geo-replication
>>>
>>> On 09/02/2015 03:12 AM, Aravinda wrote:
>>> > Geo-replication and Sharding Team today discussed about the
>>> approach
>>> > to make Sharding aware Geo-replication. Details are as below
>>> >
>>> > Participants: Aravinda, Kotresh, Krutika, Rahul Hinduja, Vijay
>>> Bellur
>>> >
>>> > - Both Master and Slave Volumes should be Sharded Volumes with
>>> same
>>> > configurations.
>>>
>>> If I am not mistaken, geo-rep supports replicating to a non-gluster
>>> local FS at the slave end. Is this correct? If so, would this
>>> limitation
>>> not make that problematic?
>>>
>>> When you state *same configuration*, I assume you mean the sharding
>>> configuration, not the volume graph, right?
>>>
>>> That is correct. The only requirement is for the slave to have shard
>>> translator (for, someone needs to present aggregated view of the file to
>>> the READers on the slave).
>>> Also the shard-block-size needs to be kept same between master and
>>> slave. Rest of the configuration (like the number of subvols of DHT/AFR)
>>> can vary across master and slave.
>>
>>
>> Do we need to have the sharded block size the same? As I assume the file
>> carries an xattr that contains the size it is sharded with
>> (trusted.glusterfs.shard.block-size), so if this is synced across, it would
>> do. If this is true, what it would mean is that "a sharded volume needs a
>> shard supported slave to ge-rep to".
>
> Yes. Number of bricks and replica count can be different. But sharded block
> size should be same. Only the first file will have
> xattr(trusted.glusterfs.shard.block-size), Geo-rep should sync this xattr
> also to Slave. Only Gsyncd can read/write the sharded chunks. Sharded Slave
> Volume is required to understand these chunks when read(non Gsyncd clients)Even if this works I am very much is disagreement with this mechanism
of synchronization (not that I have a working solution in my head as
of now).
Hi Venky,
It is not apparent to me what issues you see with approach 2. If you could lay them out here, it would be helpful in taking the discussions further.
-Krutika
>
>>
>>>
>>> -Krutika
>>>
>>>
>>>
>>> > - In Changelog record changes related to Sharded files also. Just
>>> like
>>> > any regular files.
>>> > - Sharding should allow Geo-rep to list/read/write Sharding
>>> internal
>>> > Xattrs if Client PID is gsyncd(-1)
>>> > - Sharding should allow read/write of Sharded files(that is in
>>> .shards
>>> > directory) if Client PID is GSYNCD
>>> > - Sharding should return actual file instead of returning the
>>> > aggregated content when the Main file is requested(Client PID
>>> > GSYNCD)
>>> >
>>> > For example, a file f1 is created with GFID G1.
>>> >
>>> > When the file grows it gets sharded into chunks(say 5 chunks).
>>> >
>>> > f1 G1
>>> > .shards/G1.1 G2
>>> > .shards/G1.2 G3
>>> > .shards/G1.3 G4
>>> > .shards/G1.4 G5
>>> >
>>> > In Changelog, this is recorded as 5 different files as below
>>> >
>>> > CREATE G1 f1
>>> > DATA G1
>>> > META G1
>>> > CREATE G2 PGS/G1.1
>>> > DATA G2
>>> > META G1
>>> > CREATE G3 PGS/G1.2
>>> > DATA G3
>>> > META G1
>>> > CREATE G4 PGS/G1.3
>>> > DATA G4
>>> > META G1
>>> > CREATE G5 PGS/G1.4
>>> > DATA G5
>>> > META G1
>>> >
>>> > Where PGS is GFID of .shards directory.
>>> >
>>> > Geo-rep will create these files independently in Slave Volume and
>>> > syncs Xattrs of G1. Data can be read only when all the chunks are
>>> > synced to Slave Volume. Data can be read partially if main/first
>>> file
>>> > and some of the chunks synced to Slave.
>>> >
>>> > Please add if I missed anything. C & S Welcome.
>>> >
>>> > regards
>>> > Aravinda
>>> >
>>> > On 08/11/2015 04:36 PM, Aravinda wrote:
>>> >> Hi,
>>> >>
>>> >> We are thinking different approaches to add support in
>>> Geo-replication
>>> >> for Sharded Gluster Volumes[1]
>>> >>
>>> >> *Approach 1: Geo-rep: Sync Full file*
>>> >> - In Changelog only record main file details in the same brick
>>> >> where it is created
>>> >> - Record as DATA in Changelog whenever any addition/changes
>>> to the
>>> >> sharded file
>>> >> - Geo-rep rsync will do checksum as a full file from mount and
>>> >> syncs as new file
>>> >> - Slave side sharding is managed by Slave Volume
>>> >> *Approach 2: Geo-rep: Sync sharded file separately*
>>> >> - Geo-rep rsync will do checksum for sharded files only
>>> >> - Geo-rep syncs each sharded files independently as new files
>>> >> - [UNKNOWN] Sync internal xattrs(file size and block count)
>>> in the
>>> >> main sharded file to Slave Volume to maintain the same state as
>>> in Master.
>>> >> - Sharding translator to allow file creation under .shards
>>> dir for
>>> >> gsyncd. that is Parent GFID is .shards directory
>>> >> - If sharded files are modified during Geo-rep run may end up
>>> stale
>>> >> data in Slave.
>>> >> - Files on Slave Volume may not be readable unless all sharded
>>> >> files sync to Slave(Each bricks in Master independently sync
>>> files to
>>> >> slave)
>>> >>
>>> >> First approach looks more clean, but we have to analize the Rsync
>>> >> checksum performance on big files(Sharded in backend, accessed
>>> as one
>>> >> big file from rsync)
>>> >>
>>> >> Let us know your thoughts. Thanks
>>> >>
>>> >> Ref:
>>> >> [1]
>>> >>
>>>
>>> http://www.gluster.org/community/documentation/index.php/Features/sharding-xlator
>>> >> --
>>> >> regards
>>> >> Aravinda
>>> >>
>>> >>
>>> >> _______________________________________________
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>>> >> Gluster-devel@xxxxxxxxxxx
>>> >> http://www.gluster.org/mailman/listinfo/gluster-devel
>>> >
>>> >
>>> >
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>>> >
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>>>
>>>
>
> regards
> Aravinda
>
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