Linux server hangs

[Geofrey Rainey]

Could be many things but maybe you've got an I/O bottleneck - you're
trying to push too much stuff through a small pipe (for instance you're
I/O controller can't handle the throughput). Or it's likely that if
You've got a single disk and multiple users are reading/writing to/from
It, the disk heads simply can't do two physical tasks at once and you
Get high I/O wait times. I see the same symptoms on my own
Computer if it's doing something I/O intensive like reading or writing 
A big file, and I try to do something else at the same time, this
behaviour
Is quite normal. That's why servers should have multiple disks
configured
In a RAID array so you can utilize multiple disk heads and minimize I/O
Bottlenecks.

Install the sysstat package and type "sar 1 100", what does that say?

Example output, you can see the iowait time our server is low (we've got
An external disk array):

[root at server]# sar 1 100
Linux 2.6.18-92.1.10.el5 (server.domain)     01/30/2009

06:47:59 PM       CPU     %user     %nice   %system   %iowait    %steal
%idle
06:48:00 PM       all      6.25      0.00      2.00      0.00      0.00
91.75
06:48:01 PM       all      2.00      0.00      2.25      0.25      0.00
95.50
06:48:02 PM       all      5.50      0.00      5.25      0.00      0.00
89.25
06:48:03 PM       all      1.25      0.00      1.75      0.25      0.00
96.75

Regards,
Geofrey.

-----Original Message-----
From: redhat-list-bounces at redhat.com
[mailto:redhat-list-bounces at redhat.com] On Behalf Of Vishnu Vardhan
Reddy
Sent: Friday, 30 January 2009 6:36 p.m.
To: General Red Hat Linux discussion list
Subject: Linux server hangs

Dear All,

I just had a really bad experience with one of the IBM Server which has
Red Hat RHEL 4 WS with update 6 OS on it. It has two SATA hard disks out
of which one is of 80 GB( contains /boot, / & swap
partitions) and on other disk 250 GB single partition ( /data).

On this serve I am currently running samba, nfs, ftp services & some
embedded tools, with 20 users who works entirely on this server through
telnet, samba services, and compiles the source on this related to
embedded tools.

My problem is, if all the users are logged in through telnet, ftp and
access data through samba and perform some I/O operations like copying,
moving and deleting data, the server getting hanged for 30 seconds and
further becomes slow until the application is closed or completed, this
effects other users terminals.

As per my observation if I copy some 500 MB file from partition to
partition, from disk to disk, or when I start checkout from CVS the CPU
utilization is showing less, but server freezes for some time.
Even I cont open any file through VI, after the application is closed
the server becomes fast, all the users can work with VI editor.

Can anyone help me in this issue?

Thanks
Vishnu


      
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