[Gluster-users] Regarding the issues gluster DHT and Layouts of bricks

Subrata Ghosh subrata.ghosh at ericsson.com
Tue May 26 11:35:17 UTC 2015


Sorry for the wrong incomplete message sent by mistake earlier.

Hi Sussant,

Extremely sorry for the belated reply. Thanks  for your input. We will try having rebalance then create a set of small files with a random pattern generation and check where it falls in by DM_TYPE  DHT.

I have one short query:
We were also thinking to use (in case we need ) Translators/cluster/unify along with NUFA or ALU scheduler. However we noticed Translators/cluster/unify became  obsolete/legacy in gluster site , does it mean automatically ALU, NUFA,rr scheduler also became obsolete or not supported ? Can you please clarify ?

Is the Translators/cluster/unify is supported in 3.3.2 ( we are currently using) and following configuration would work ?

If not can you please suggest you how to use ALU/NUFA scheduler with 3.3.2 if there is any specific mechanism?

volume unify
   type cluster/unify
   subvolumes brick1 brick2 brick3 brick4
   option namespace brick-ns # should be a node which is not present in 'subvolumes'
   option scheduler NUFA/ALU/rr    # NUFA/ALU or Simple round-robin scheduler
end-volume

Thanks again for your time and advice.

Regards,

-----Original Message-----
From: Susant Palai [mailto:spalai at redhat.com]
Sent: Thursday, May 21, 2015 6:17 PM
To: Subrata Ghosh
Cc: gluster-devel at gluster.org; gluster-users at gluster.org; Nobin Mathew; Vijay Bellur
Subject: Re: Regarding the issues gluster DHT and Layouts of bricks

Commets inline.

----- Original Message -----
> From: "Subrata Ghosh" <subrata.ghosh at ericsson.com<mailto:subrata.ghosh at ericsson.com>>
> To: gluster-devel at gluster.org<mailto:gluster-devel at gluster.org>, gluster-users at gluster.org<mailto:gluster-users at gluster.org>
> Cc: "Nobin Mathew" <nobin.mathew at ericsson.com<mailto:nobin.mathew at ericsson.com>>, "Susant Palai" <spalai at redhat.com<mailto:spalai at redhat.com>>, "Vijay Bellur"
> <vbellur at redhat.com<mailto:vbellur at redhat.com>>
> Sent: Thursday, 21 May, 2015 4:26:05 PM
> Subject: Regarding the issues gluster DHT and  Layouts of bricks
>
>
> Hi  All,
>
> Could you please guide us  to solve the following DHT and brick layout
> problem we are  dealing with ? Questions are marked bold.
>
> Problem statement :
>
>
> 1.      We have a requirement to achieve maximum write and read performance
> and we have to meet some committed performance metrics.
>
>                Our goal is to place each file into different bricks to get
>                optimal performance and also observer the nature of the
>                throughput , hence need to have a mechanism  to generate
>                different hash using gluster glusterfs.gf_dm_hashfn,
> (assuming number of files are : N , Number of Bricks :N)  to place
> spate bricks.
>
>
> -        How to make sure each file has different hash and   falls to
> different bricks ?
>
>
>
> -        Other way to put the question if I  know the range of the brick
> layout or more precisely if I know the  hex value of the desired hash
> ( so that it will be placed desired brick)  that we need to generate
> from Davis-Meyer algorithm used in gluster,  Can we create a file name
> such that, that also solve our problem to some extent?
>
>
> 2.      We tried to experiment to see  how a file in gluster is decided to be
> placed in a particular brick following gluster glusterfs.gf_dm_hashfn
> and took some idea from
>        some articles  like
>        http://gluster.readthedocs.org/en/latest/Features/dht/ ,
>        https://joejulian.name/blog/dht-misses-are-expensive/ page which
>        describes layout for that brick  and calculate a hash for the file.
>
>
>         To minimize collisions or generating different hash in such way to
>         place each file in different bricks ( file 1 => brick A, file 2 =>
>         Brick B, file 3=>  Brick C, file 4 => brick D)
>
>                We use kind of similar script to get the hash value for
> a file
>
> def gf_dm_hashfn(filename):
>     return ctypes.c_uint32(glusterfs.gf_dm_hashfn(
>         filename,
>         len(filendame)))
>
> if __name__ == "__main__":
>     print hex(gf_dm_hashfn(sys.argv[1]).value)
>
> We can then calculate the hash for a filename:
> # python gf_dm_hash.py file1
> 0x99d1b6fL
>
>
> Extended attribute is fetch to check the range and try to match the
> above generated hash value.
>
> getfattr -n trusted.glusterfs.dht -e hex file1
>
>
>       However we are not able to exactly follow till this point ,  how the
>       hash value matched to one of the layout assignments, to yield what we
>       call a hashed location.
>
>
> -        My question is if I  know the range of brick lay out ( say
> 0xc0000000 to  0xffffffff, is range  select a hash 0xc0070000 ) where
> to be placed the next file can we generate the name ( kind of reverse
> of  gluster
> glusterfs.gf_dm_hashfn) ?

I am not aware of any such mechanism.  You will have to generate file names manually and run them through your script to check whether it falls in the brick range.

>
> PS :  Susant : Can you throw some light or suggest  a method we are
> trying to solve.
>
> Thanks for your time.
>
>
> Best Regards,
> Subrata Ghosh
>
>
>
>
>
>
>
Regards,
Susant

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