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Top Forums UNIX for Dummies Questions & Answers Raid0 array stresses only 1 disk out of 3 Post 302970987 by chebarbudo on Thursday 14th of April 2016 10:45:21 AM
Old 04-14-2016
Hi guys,

Thank you very much for your contributions.

First of all, my problem does not happen any more. I created the raid with sdb, sdc and sdd on April 11 at 09:35.
Until 11:32, sdd was very busy, then until 14:51, sdc was very busy.
Since then (3 days), the 3 disks are always under the same moderate load altogether (0-20%). The server is used by 5 graphic designers manipulating quite large files (100M-2G).

I ran some tests and the results leave me quite puzzled. So I created simultaneously 10 files. 1GB each. But all the load went on sda. Leaving sdb, sdc and sdd with a moderate 20% load.

The command:
Code:
for i in {1..10}; do
  file=$(mktemp /galaxy/XXXXXXX)
  echo $file >> /galaxy/dd.files
  dd if=/dev/zero of=$file bs=1G count=1 &
  echo $!    >> /galaxy/dd.pids
done

The output of dstat:
Code:
----system---- sda--sdb--sdc--sdd-
     time     |util:util:util:util
14-04 15:56:30|  21:   0:   0:   0
14-04 15:57:00| 100:   0:   0:   0
14-04 15:57:30| 101:   0:   0:   0
14-04 15:58:00| 100:   2:   2:   1
14-04 15:58:30| 101:   3:   4:   2
14-04 15:59:00| 102:   4:   5:   4
14-04 15:59:30|  98:   2:   3:   2
14-04 16:00:00| 100:   4:   4:   2
14-04 16:00:30| 103:  16:  16:  15
14-04 16:01:00|  98:  16:  17:  15
14-04 16:01:30| 101:  15:  15:  15
14-04 16:02:00|  99:   9:   8:   8
14-04 16:02:30| 100:   3:   4:   3
14-04 16:03:00| 100:   2:   4:   3
14-04 16:03:30| 104:   4:   4:   3
14-04 16:04:00|  95:   4:   4:   3
14-04 16:04:30| 100:   3:   4:   2
14-04 16:05:00| 101:   3:   4:   3
14-04 16:05:30|  99:  12:  13:  12
14-04 16:06:00| 102:  20:  22:  18
14-04 16:06:30|  98:  17:  19:  18
14-04 16:07:00| 101:   7:   9:   8
14-04 16:07:30|  99:   4:   5:   3
14-04 16:08:00| 102:   4:   5:   3
14-04 16:08:30|  98:   3:   5:   3
14-04 16:09:00| 100:   5:   7:   5
14-04 16:09:30| 101:   5:   5:   4
14-04 16:10:00| 100:   4:   4:   2
14-04 16:10:30| 100:  17:  18:  16
14-04 16:11:01| 105:  16:  20:  16
14-04 16:11:30|  95:  15:  17:  17
14-04 16:12:00| 100:  12:  11:  10
14-04 16:12:30|  34:  15:  16:  14

Is /dev/zero an actual file of sda?
How do you interpret the results?

Regards
Santiago
 

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stripe(8)						      System Manager's Manual							 stripe(8)

NAME
stripe - Stripes a file across several volumes in a file domain SYNOPSIS
/usr/sbin/stripe -n volume_count filename OPTIONS
Specifies the number of volumes the striped file crosses. The number of volumes must be greater than one. OPERANDS
Specifies the name of the file to stripe. DESCRIPTION
The stripe utility enables you to improve the read/write performance of a file. The stripe utility directs a zero-length file (a file with no data written to it yet) to be spread evenly across several volumes within a file domain. As data is appended to the file, the data is spread across the volumes. AdvFS determines the number of pages per stripe segment and alternates the segments among the disks in a sequen- tial pattern. Existing, nonzero-length files cannot be striped using the stripe utility. To stripe an existing file, create a new file, use the stripe utility to stripe the new file, and copy the contents of the file you want to stripe into the new striped file. After copying the file, delete the nonstriped file. Once a file is striped, you cannot use the stripe utility to modify the number of disks that a striped file crosses. To change the volume count of a striped file, you can create a second file with a new volume count, and then copy the contents of the first file into the second file. After copying the file, delete the first file. RESTRICTIONS
You cannot stripe a nonzero-length file or a file that is already striped. EXAMPLES
The following example stripes the file abc across three volumes in the same file domain: # stripe -n 3 abc The following example stripes an existing, nonzero-length file, foo, across three volumes in the same domain. First a new file, newfoo, is created and striped. Then, the contents of file foo are copied to the new, striped file: # touch newfoo # stripe -n 3 newfoo # cp foo newfoo SEE ALSO
advfs(4), showfile(8) stripe(8)
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