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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "CassandraHardware" by RyanKing
Date Mon, 26 Apr 2010 19:10:10 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Cassandra Wiki" for change notification.

The "CassandraHardware" page has been changed by RyanKing.
http://wiki.apache.org/cassandra/CassandraHardware?action=diff&rev1=12&rev2=13

--------------------------------------------------

  
  So to summarize, if you use a different device for your `CommitLogDirectory` it needn't
be large, but it should be fast enough to receive all of your writes (as appends, i.e., sequential
i/o). Then, use one or more devices for `DataFileDirectories` and make sure they are both
large enough to house all of your data, and fast enough to both satisfy reads that are not
cached in memory and to keep up with flushing and compaction.
  
- As covered in [[MemtableSSTable]], compactions can require up to 100% of your in-use space
temporarily in the worst case, free on a single volume (that is, in a data file directory).
 So if you are going to be approaching 50% or more of your disks' capacity, you should raid0
your data directory volumes.  B. Todd Burruss adds on the mailing list, "With the file sizes
we're talking about with cassandra and other database products, the [raid] stripe size doesn't
seem to matter.  Mine is set to 128k, which produced the same results as 16k and 256k."
+ As covered in [[MemtableSSTable]], compactions can require up to 100% of your in-use space
temporarily in the worst case, free on a single volume (that is, in a data file directory).
 So if you are going to be approaching 50% or more of your disks' capacity, you should raid0
your data directory volumes.  B. Todd Burruss adds on the mailing list, "With the file sizes
we're talking about with cassandra and other database products, the [raid] stripe size doesn't
seem to matter.  Mine is set to 128k, which produced the same results as 16k and 256k." In
addition to giving you capacity for compactions, raid0 will help eliminate io hotspots (cassandra
does nothing ensure load balance among data directories).
  
  On ext2/ext3 the maximum file size is 2TB, even on a 64 bit kernel.  On ext4 that goes up
to 16TB.  Since Cassandra can use almost half your disk space on a single file, if you are
raiding large disks together you may want to use XFS instead, particularly if you are using
a 32-bit kernel.  XFS file size limits are 16TB max on a 32 bit kernel, and basically unlimited
on 64 bit.
  

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