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Full Discussion: Disk Performance
Operating Systems Linux Disk Performance Post 302961567 by jimthompson on Tuesday 1st of December 2015 10:28:34 AM
Old 12-01-2015
Disk Performance

I have a freshly installed Oracle Linux 7.1 ( akin to RHEL ) server.

However after installing some Oracle software, I have noticed that my hard disk light is continually on and the system performance is slow.

So I check out SAR and IOSTAT

Code:
lab3:/root>iostat
Linux 3.8.13-55.1.6.el7uek.x86_64 (lab3)        01/12/15        _x86_64_        (2 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          21.33    0.00    2.66   41.71    0.00   34.30

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda             100.94      1928.77       653.97  110966874   37624674
sdb              53.08       929.61      3510.79   53482763  201984646
dm-0            438.70      1351.24       653.67   77740019   37607217
dm-1              0.01         0.02         0.00       1396          0
dm-2              4.93       577.01         0.27   33196938      15409

lab3:/root>sar 5 5
Linux 3.8.13-55.1.6.el7uek.x86_64 (lab3)        01/12/15        _x86_64_        (2 CPU)

15:19:06        CPU     %user     %nice   %system   %iowait    %steal     %idle
15:19:11        all      0.50      0.00      0.40      3.52      0.00     95.58
15:19:16        all      0.50      0.00      0.50      2.21      0.00     96.78
15:19:21        all      0.70      0.00      0.40      1.81      0.00     97.08
15:19:26        all      0.40      0.00      0.40      3.73      0.00     95.46
15:19:31        all      0.50      0.00      0.50     13.29      0.00     85.70
Average:        all      0.52      0.00      0.44      4.91      0.00     94.12

Now I only have 2 disks in my server i.e. /dev/sda and /dev/sdb

Q1. Why does Linux create dm-0,dm-1 and dm-2 as separate devices ( albeit I guess these are virtual devices via Device Manager ?
As far as I can tell these are the Oracle Linux Home, the Swap Device and
the Oracle Linux Root - however Idon't see a command directly linking dm-0, and dm-1 which the /home and / mount points

Q2. How do you tell if the dm-0, dm-1 and dm-2 are using the sda or sdb device ?

Q3. I see dm-0 ( Linux Home ) is experiencing a high rate of tps ( transactions per second ? ) whereas the sda device ( which I believe dm-0 is ultamately on ) is experiencing a high amount of data read - is this where my performance problem resides ?

Q4. Is there a way to tell which mounted file system is performing poorly ?

Q5. Why when I increase the Swap from 3 Gb to 19 Gb, I do this by adding a swap file ? Why is the 3 Gb shown as a swap device but the additional 16 Gb is not shown as a device ?

Code:
lab3:/root>swapon
NAME       TYPE      SIZE USED PRIO
/swapfile1 file       16G 6.8G   -1
/dev/dm-1  partition   3G   0B   -2

any help greatly appreciated
Jim

Last edited by Scrutinizer; 12-01-2015 at 12:18 PM.. Reason: Code tags
 

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Apache::Session::Oracle(3pm)				User Contributed Perl Documentation			      Apache::Session::Oracle(3pm)

NAME
Apache::Session::Oracle - An implementation of Apache::Session SYNOPSIS
use Apache::Session::Oracle; #if you want Apache::Session to open new DB handles: tie %hash, 'Apache::Session::Oracle', $id, { DataSource => 'dbi:Oracle:sessions', UserName => $db_user, Password => $db_pass, Commit => 1 }; #or, if your handles are already opened: tie %hash, 'Apache::Session::Oracle', $id, { Handle => $dbh, Commit => 1 }; DESCRIPTION
This module is an implementation of Apache::Session. It uses the Oracle backing store and no locking. See the example, and the documentation for Apache::Session::Store::Oracle for more details. USAGE
The special Apache::Session argument for this module is Commit. You MUST provide the Commit argument, which instructs this module to either commit the transaction when it is finished, or to simply do nothing. This feature is provided so that this module will not have adverse interactions with your local transaction policy, nor your local database handle caching policy. The argument is mandatory in order to make you think about this problem. This module also respects the LongReadLen argument, which specifies the maximum size of the session object. If not specified, the default maximum is 8 KB. AUTHOR
This module was written by Jeffrey William Baker <jwbaker@acm.org>. SEE ALSO
Apache::Session::File, Apache::Session::Flex, Apache::Session::DB_File, Apache::Session::Postgres, Apache::Session perl v5.10.1 2010-10-18 Apache::Session::Oracle(3pm)
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