[Gluster-users] default cluster.stripe-block-size for striped volumes on 3.0.x vs 3.3 beta (128kb), performance change if i reduce to a smaller block size?

[Sabuj Pattanayek]

Hi,

I've been migrating data from an old striped 3.0.x gluster install to
a 3.3 beta install. I copied all the data to a regular XFS partition
(4K blocksize) from the old gluster striped volume and it totaled
9.2TB. With the old setup I used the following option in a "volume
stripe" block in the configuration file in a client :

volume stripe
  type cluster/stripe
  option block-size 2MB
  subvolumes ....
end-volume

IIRC, the data was using up about the same space on the old striped
volume (9.2T) . While copying the data back to the new v3.3 striped
gluster volume on the same 5 servers/same brick filesystems (XFS w/4K
blocksize), I noticed that the amount stored on disk increased by 5x.

Currently if I do a du -sh on the gluster fuse mount of the new
striped volume I get 4.3TB (I haven't finished copying all 9.2TB of
data over, stopped it prematurely because it's going to use up all the
physical disk it seems if I let it keep going). However, if I do a du
-sh at the filesystem / brick level on each of the 5 directories on
the 5 servers that store the striped data, it shows that each one is
storing 4.1TB. So basically, 4.3TB of data from a 4K block size FS
took up 20.5TB of storage on a 128KB block size striped gluster
volume. What is the correlation between the " option block-size"
setting on client configs in cluster/stripe blocks in 3.0.x vs the
cluster.stripe-block-size parameter in 3.3? If these settings are
talking about what I think they mean, then basically a file that is 1M
in size would be written out to the stripe in 128KB chunks across N
servers, i.e. 128/N KB of data per brick? What happens when the stripe
block size isn't evenly divisible by N (e.g. 128/5 = 25.6). If the old
block-size and new stripe-block-size options are describing the same
thing, then wouldn't a 2MB block size from the old config cause more
storage to be used up vs a 128KB block size?

Thanks,
Sabuj