Commets inline. ----- Original Message ----- > From: "Subrata Ghosh" <subrata.ghosh@xxxxxxxxxxxx> > To: gluster-devel@xxxxxxxxxxx, gluster-users@xxxxxxxxxxx > Cc: "Nobin Mathew" <nobin.mathew@xxxxxxxxxxxx>, "Susant Palai" <spalai@xxxxxxxxxx>, "Vijay Bellur" > <vbellur@xxxxxxxxxx> > 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 _______________________________________________ Gluster-users mailing list Gluster-users@xxxxxxxxxxx http://www.gluster.org/mailman/listinfo/gluster-users
