HI, guys:
I have a 15 node cluster, each node has 12 SATA disk which is 1TB, I make soft
RAID5 on 11 disk to create a large data partition(md0):
[r...@xxxx ~]# mount
/dev/sda2 on / type ext2 (rw)
none on /proc type proc (rw)
none on /sys type sysfs (rw)
none on /dev/pts type devpts (rw,gid=5,mode=620)
usbfs on /proc/bus/usb type usbfs (rw)
/dev/sda3 on /home type ext2 (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
/dev/md0 on /home/store0 type ext2 (rw)
[r...@xxxx ~]# cat /proc/mdstat
Personalities : [raid5]
md0 : active raid5 sdf1[4] sdb1[0] sdl1[10] sdk1[9] sdj1[8] sdi1[7] sdh1[6]
sdg1[5] sde1[3] sdd1[2] sdc1[1]
9767599360 blocks level 5, 64k chunk, algorithm 2 [11/11] [UUUUUUUUUUU]
unused devices: <none>
[r...@xxx ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda2 9076396 4153868 4922528 46% /
/dev/sda3 951353164 761568 902265668 1% /home
/dev/md0 9729280288 3131116128 6598164160 33% /home/store0
storage-conf.xml:
……
<CommitLogDirectory>/home/store0/cassandra/commitlog</CommitLogDirectory>
<DataFileDirectories>
<DataFileDirectory>/home/store0/cassandra/data</DataFileDirectory>
</DataFileDirectories>
<CalloutLocation>/home/store0/cassandra/callouts</CalloutLocation>
<StagingFileDirectory>/home/store0/cassandra/staging</StagingFileDirectory>
……
Problem is：
(1) A cluster cannot be enlarge(add more node into cluster) if it already
used more than half capacity:
If every node has data more than it’s half capacity , the admin may not
bootstrapping new node into cluster,
because old nodes must strip data belong to new node through anti-compaction,
the process will create a large tmp SSTable
file (for streaming), which may large than free disk space ( of one node ).
(2) Any node cannot have load large than 3TB:
Because the tmp SSTable file may large than 2TB, which is invalid on ext2/3 fs.
Question is:
(1) Is cassandra designed to waste half of it’s capacity?
(2) How to use node has 12 1TB disk??
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