[CentOS] RAID on Email Server

Matt lm7812 at gmail.com
Fri Oct 10 18:13:39 UTC 2008


>> I have an email server running Exim, Dovecot, Spamassassin, Clam, etc.
>> on Centos 4.x 32bit.  On occasion I have disk I/O problems.  Its
>> handling several domains and alot of email.  Its currently on a single
>> SATA drive.  I am thinking of moving too 3 drives with RAID 1 for
>> redundancy.  RAID 1 will help me on reads but do nothing on writes as
>> I understand.  I am thinking the majority of my I/O is read though
>> not?  I imagine quotta checks and all that being done and everytime a
>> user checks there email every message in the inbox must be read.
>>
>> I guess I am asking if RAID 1 will help my I/O problem much?
>>
>> [root at server ~]# w
>>  12:04:02 up  2:01,  1 user,  load average: 7.02, 7.47, 11.84
>> USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
>> root     pts/0    208.92.169.4.ppp 11:25    0.00s  0.02s  0.00s w
>> [root at server ~]# vmstat
>> procs -----------memory---------- ---swap-- -----io---- --system--
>> ----cpu----
>>  r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy
>> id wa
>>  0  2      0 1558496 456916 1087224    0    0   198   749  795   537 18  4
>> 27 50
>>
>> The above is when its running pretty good.
>>
>
> can you paste the output of `iostat -x 5 5` while its busy ?   this will
> show definateively how busy your disks are...
> the first sample from vmstat, iostat, etc only shows the AVERAGE since the
> system booted.   the 2nd and beyond samples are the average over the time
> intervals specified (5 5 means 5 seconds, 5 samples)
>
> oh, if you don't have iostat, its part of package sysstat, so `yum install
> sysstat`

Right now its running pretty good but here it is.

[root at server ~]# w
 13:11:02 up  3:08,  2 users,  load average: 4.03, 5.71, 5.51

avg-cpu:  %user   %nice    %sys %iowait   %idle
           2.80    0.00    1.60   58.10   37.50

Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s    rkB/s    wkB/s
avgrq-sz avgqu-sz   await  svctm  %util
sda          0.60 142.80 67.20 170.20  678.40 2292.80   339.20
1146.40    12.52   118.53  615.66   4.21  99.92
sda1         0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00
    0.00     0.00    0.00   0.00   0.00
sda2         0.60 142.80 67.20 170.20  678.40 2292.80   339.20
1146.40    12.52   118.53  615.66   4.21  99.92
sdb          0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00
    0.00     0.00    0.00   0.00   0.00
sdb1         0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00
    0.00     0.00    0.00   0.00   0.00
dm-0         0.00   0.00 67.40 286.20  678.40 2289.60   339.20
1144.80     8.39   163.02  582.40   2.83  99.94
dm-1         0.00   0.00  0.00  0.00    0.00    0.00     0.00     0.00
    0.00     0.00    0.00   0.00   0.00


sar also.

10:02:56 AM       LINUX RESTART

10:10:04 AM       CPU     %user     %nice   %system   %iowait     %idle
10:20:01 AM       all     13.87      0.00      2.45     59.20     24.49
10:30:03 AM       all     22.26      0.00      3.68     53.51     20.54
10:40:01 AM       all     20.58      0.00      3.78     55.40     20.24
10:50:04 AM       all     22.20      0.00      5.23     52.67     19.91
11:00:05 AM       all     21.58      0.00      4.72     51.81     21.89
11:10:01 AM       all     18.14      0.00      4.52     56.91     20.43
11:20:03 AM       all     21.42      0.00      4.59     47.20     26.79
11:30:02 AM       all     19.22      0.00      4.48     53.86     22.44
11:40:04 AM       all     17.59      0.00      4.82     51.61     25.98
11:50:02 AM       all     15.88      0.00      4.67     45.74     33.71
12:00:01 PM       all     13.32      0.00      2.73     25.72     58.23
12:10:02 PM       all     16.98      0.00      4.54     53.14     25.35
12:20:01 PM       all     17.31      0.00      3.45     47.80     31.44
12:30:01 PM       all     19.45      0.00      4.08     36.47     40.00
12:40:01 PM       all     13.79      0.00      4.39     44.83     36.99
12:50:01 PM       all     12.18      0.00      3.93     30.16     53.73
01:00:01 PM       all     11.53      0.00      2.38     20.96     65.12
Average:          all     17.49      0.00      4.03     46.29     32.19

A while after the reboot it straightened its self out.  Yesterday "w"
was indicatining load average of like 120 or more at times.  Today
after reboot all is good.

Matt


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