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Imbalanced storage distribution over JBOD devices
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Description

In the RESTBase Cassandra cluster, data distributed over the JBOD devices, isn't always very balanced (some are more imbalanced than others). For example:

restbase1007
~# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev             10M     0   10M   0% /dev
tmpfs            26G  2.5G   23G  10% /run
/dev/md0         28G  4.5G   22G  18% /
tmpfs            63G     0   63G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            63G     0   63G   0% /sys/fs/cgroup
/dev/sdd4       893G  544G  349G  61% /srv/sdd4
/dev/sdb4       893G  528G  365G  60% /srv/sdb4
/dev/sdc4       893G  587G  306G  66% /srv/sdc4
/dev/sda4       893G  368G  525G  42% /srv/sda4
/dev/sde4       893G  278G  615G  32% /srv/sde4
/dev/md2         46G   23G   21G  52% /srv/cassandra/instance-data

~# du -shc /srv/sd[a-e]4/cassandra-{a,b,c}
105G	/srv/sda4/cassandra-a
172G	/srv/sdb4/cassandra-a
205G	/srv/sdc4/cassandra-a
113G	/srv/sdd4/cassandra-a
53G	/srv/sde4/cassandra-a
76G	/srv/sda4/cassandra-b
147G	/srv/sdb4/cassandra-b
171G	/srv/sdc4/cassandra-b
189G	/srv/sdd4/cassandra-b
106G	/srv/sde4/cassandra-b
188G	/srv/sda4/cassandra-c
210G	/srv/sdb4/cassandra-c
212G	/srv/sdc4/cassandra-c
243G	/srv/sdd4/cassandra-c
120G	/srv/sde4/cassandra-c
2.3T	total
~#

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Eevans created this task.Jun 4 2018, 3:21 PM
Restricted Application added a subscriber: Aklapper. · View Herald TranscriptJun 4 2018, 3:21 PM
Eevans triaged this task as Normal priority.Jun 4 2018, 3:21 PM
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mobrovac renamed this task from eobaaaaaaa to Imbalanced storage distribution over JBOD devices.Jul 1 2018, 11:19 AM
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This imbalance seems to resolved itself.

P8999 Masterwork From Distant Lands
1restbase1016.eqiad.wmnet: /dev/sdc4 1.4T 298G 1.1T 21% /srv/sdc4
2restbase1016.eqiad.wmnet: /dev/sda4 1.4T 299G 1.1T 22% /srv/sda4
3restbase1016.eqiad.wmnet: /dev/sdd4 1.4T 304G 1.1T 22% /srv/sdd4
4restbase1016.eqiad.wmnet: /dev/sdb4 1.4T 313G 1.1T 23% /srv/sdb4
5restbase1019.eqiad.wmnet: /dev/sdb4 1.7T 382G 1.3T 23% /srv/sdb4
6restbase1019.eqiad.wmnet: /dev/sda4 1.7T 369G 1.3T 22% /srv/sda4
7restbase1019.eqiad.wmnet: /dev/sdc4 1.7T 360G 1.3T 22% /srv/sdc4
8restbase1020.eqiad.wmnet: /dev/sda4 1.7T 393G 1.3T 24% /srv/sda4
9restbase1020.eqiad.wmnet: /dev/sdb4 1.7T 402G 1.3T 24% /srv/sdb4
10restbase1020.eqiad.wmnet: /dev/sdc4 1.7T 419G 1.3T 25% /srv/sdc4
11restbase1021.eqiad.wmnet: /dev/sda4 1.7T 365G 1.3T 22% /srv/sda4
12restbase1021.eqiad.wmnet: /dev/sdb4 1.7T 339G 1.4T 21% /srv/sdb4
13restbase1021.eqiad.wmnet: /dev/sdc4 1.7T 360G 1.3T 22% /srv/sdc4
14restbase1017.eqiad.wmnet: /dev/sda4 1.4T 258G 1.2T 19% /srv/sda4
15restbase1017.eqiad.wmnet: /dev/sdb4 1.4T 270G 1.2T 19% /srv/sdb4
16restbase1017.eqiad.wmnet: /dev/sdc4 1.4T 268G 1.2T 19% /srv/sdc4
17restbase1017.eqiad.wmnet: /dev/sdd4 1.4T 280G 1.2T 20% /srv/sdd4
18restbase1022.eqiad.wmnet: /dev/sdc4 1.7T 386G 1.3T 23% /srv/sdc4
19restbase1022.eqiad.wmnet: /dev/sda4 1.7T 373G 1.3T 23% /srv/sda4
20restbase1022.eqiad.wmnet: /dev/sdb4 1.7T 382G 1.3T 23% /srv/sdb4
21restbase1023.eqiad.wmnet: /dev/sdb4 1.7T 373G 1.3T 23% /srv/sdb4
22restbase1023.eqiad.wmnet: /dev/sdc4 1.7T 388G 1.3T 23% /srv/sdc4
23restbase1023.eqiad.wmnet: /dev/sda4 1.7T 393G 1.3T 24% /srv/sda4
24restbase1024.eqiad.wmnet: /dev/sda4 1.7T 358G 1.4T 22% /srv/sda4
25restbase1024.eqiad.wmnet: /dev/sdb4 1.7T 362G 1.3T 22% /srv/sdb4
26restbase1024.eqiad.wmnet: /dev/sdc4 1.7T 400G 1.3T 24% /srv/sdc4
27restbase1018.eqiad.wmnet: /dev/sdc4 1.4T 296G 1.1T 21% /srv/sdc4
28restbase1018.eqiad.wmnet: /dev/sda4 1.4T 302G 1.1T 22% /srv/sda4
29restbase1018.eqiad.wmnet: /dev/sdb4 1.4T 294G 1.2T 21% /srv/sdb4
30restbase1018.eqiad.wmnet: /dev/sdd4 1.4T 283G 1.2T 20% /srv/sdd4
31restbase1025.eqiad.wmnet: /dev/sdc4 1.7T 397G 1.3T 24% /srv/sdc4
32restbase1025.eqiad.wmnet: /dev/sdb4 1.7T 369G 1.3T 22% /srv/sdb4
33restbase1025.eqiad.wmnet: /dev/sda4 1.7T 383G 1.3T 23% /srv/sda4
34restbase1026.eqiad.wmnet: /dev/sda4 1.7T 397G 1.3T 24% /srv/sda4
35restbase1026.eqiad.wmnet: /dev/sdb4 1.7T 386G 1.3T 23% /srv/sdb4
36restbase1026.eqiad.wmnet: /dev/sdc4 1.7T 422G 1.3T 25% /srv/sdc4
37restbase1027.eqiad.wmnet: /dev/sdb4 1.7T 379G 1.3T 23% /srv/sdb4
38restbase1027.eqiad.wmnet: /dev/sda4 1.7T 396G 1.3T 24% /srv/sda4
39restbase1027.eqiad.wmnet: /dev/sdc4 1.7T 362G 1.3T 22% /srv/sdc4

Much has changed since this issue was originally opened, most significantly, we no longer make use of wide rows. I suspect that what appeared to be an imbalance in placement was actually the result of the distribution of row sizes.

I propose we close this.

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