On 08/12/2009 01:24 PM, Hiren Joshi wrote:
36 partitions on each server - the word "partition" is ambiguous. Are
they 36 separate drives? Or multiple partitions on the same drive. If
multiple partitions on the same drive, this would be a bad
idea, as it
would require the disk head to move back and forth between the
partitions, significantly increasing the latency, and therefore
significantly reducing the performance. If each partition is
on its own
drive, you still won't see benefit unless you have many clients
concurrently changing many different files. In your above case, it's
touching a single file in sequence, and having a cluster is
costing you
rather than benefitting you.
We went with 36 partitions (on a single raid 6 drive) incase we got file
system corruption, it would take less time to fsck a 100G partition than
a 3.6TB one. Would a 3.6TB single disk be better?
Putting 3.6 TB on a single disk sounds like a lot of eggs in one basket. :-)
If you are worried about fsck, I would definitely do as the other poster
suggested and use a journalled file system. This nearly eliminates the
fsck time for most situations. This would be whether using 100G
partitions or using 3.6T partitions. In fact, there is very few reasons
not to use a journalled file system these days.
As for how to deal with data on this partition - the file system is
going to have a better chance of placing files close to each other, than
setting up 36 partitions and having Gluster scatter the files across all
of them based on a hash. Personally, I would choose 4 x 1 Tbyte drives
over 1 x 3.6 Tbyte drive, as this nearly quadruples my bandwidth and for
highly concurrent loads, nearly divides by four the average latency to
access files.
But, if you already have the 3.6 Tbyte drive, I think the only
performance-friendly use would be to partition it based upon access
requirements, rather than a hash (random). That is, files that are
accessed frequently should be clustered together at the front of a disk,
files accessed less frequently could be in the middle, and files
accessed infrequently could be at the end. This would be a three
partition disk. Gluster does not have a file system that does this
automatically (that I can tell), so it would probably require a software
solution on your end. For example, I believe dovecot (IMAP server)
allows an "alternative storage" location to be defined, so that
infrequently read files can be moved to another disk, and it knows to
check the primary storage first, and fall back to the alternative
storage after.
It you can't break up your storage by access patterns, then I think a
3.6 Tbyte file system might still be the next best option - it's still
better than 36 partitions. But, make sure you have a good file system on
it, that scales well to this size.
Cheers,
mark
--
Mark Mielke<m...@mielke.cc>
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