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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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PARTX(8)						       System Administration							  PARTX(8)

NAME
partx - tell the Linux kernel about the presence and numbering of on-disk partitions SYNOPSIS
partx [-a|-d|-s] [-t TYPE] [-n M:N] [-] disk partx [-a|-d|-s] [-t TYPE] partition [disk] DESCRIPTION
Given a device or disk-image, partx tries to parse the partition table and list its contents. It optionally adds or removes partitions. The disk argument is optional when a partition argument is provided. To force scanning a partition as if it were a whole disk (for example to list nested subpartitions), use the argument "-". For example: partx --show - /dev/sda3 This will see sda3 as a whole-disk rather than a partition. This is not an fdisk program -- adding and removing partitions does not change the disk, it just tells the kernel about the presence and numbering of on-disk partitions. OPTIONS
-a, --add Add the specified partitions, or read the disk and add all partitions. -b, --bytes Print the SIZE column in bytes rather than in human-readable format. -d, --delete Delete the specified partitions or all partitions. -g, --noheadings Do not print a header line. -l, --list List the partitions. Note that all numbers are in 512-byte sectors. This output format is DEPRECATED in favour of --show. Don't use it in newly written scripts. -o, --output list Define the output columns to use for --show and --raw output. If no output arrangement is specified, then a default set is used. Use --help to get list of all supported columns. -r, --raw Use the raw output format. -s, --show List the partitions. All numbers (except SIZE) are in 512-byte sectors. The output columns can be rearranged with the --output option. -t, --type type Specify the partition table type -- aix, bsd, dos, gpt, mac, minix, sgi, solaris_x86, sun, ultrix or unixware. -n, --nr M:N Specify the range of partitions. For backward compatibility also the format <M-N> is supported. The range may contain negative numbers, for example "--nr :-1" means the last partition, and "--nr -2:-1" means the last two partitions. Supported range specifi- cations are: <M> Specifies just one partition (e.g. --nr 3). <M:> Specifies lower limit only (e.g. --nr 2:). <:N> Specifies upper limit only (e.g. --nr :4). <M:N> or <M-N> Specifies lower and upper limits (e.g. --nr 2:4). EXAMPLES
partx --show /dev/sdb3 partx --show --nr 3 /dev/sdb partx --show /dev/sdb3 /dev/sdb All three commands list partition 3 of /dev/sdb. partx --show - /dev/sdb3 Lists all subpartitions on /dev/sdb3 (the device is used as whole-disk). partx -o START -g --nr 3 /dev/sdb Prints the start sector of partition 5 on /dev/sda without header. partx -o SECTORS,SIZE /dev/sda5 /dev/sda Lists the length in sectors and human-readable size of partition 5 on /dev/sda. partx --add --nr 3:5 /dev/sdd Adds all available partitions from 3 to 5 (inclusive) on /dev/sdd. partx -d --nr :-1 /dev/sdd Removes the last partition on /dev/sdd. SEE ALSO
addpart(8), delpart(8), fdisk(8), parted(8), partprobe(8) AUTHORS
Davidlohr Bueso <dave@gnu.org> Karel Zak <kzak@redhat.com> The original version was written by Andries E. Brouwer <aeb@cwi.nl>. AVAILABILITY
The partx command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/. util-linux February 2011 PARTX(8)
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