Raid0 array stresses only 1 disk out of 3


 
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# 8  
Old 04-14-2016
You are producing stats of the disks, but the stripe is made with partitions on those disks.. Are there other partitions on those disks. Also, what filesystem was created on the striped md device and where is it mounted?

/dev/zero is a character (c) device on the root filesystem in the directory /dev

What output does df produce?
# 9  
Old 04-14-2016
Hi Scrutinizer,

Thanks for your contribution.

sda contains /, /tmp, /usr, /var and swap.
sdb, sdc and sdd contain only 1 partition each: sdb1, sdc1 and sdd1.
md0 is made of sdb1, sdc1 and sdd1

Output of df :
Code:
Filesystem                                              1K-blocks       Used  Available Use% Mounted on
rootfs                                                    1922416     337512    1487248  19% /
udev                                                        10240          0      10240   0% /dev
tmpfs                                                      403248       5800     397448   2% /run
/dev/disk/by-uuid/314e823f-91b2-42f9-9a4b-d66b5e202e27    1922416     337512    1487248  19% /
tmpfs                                                        5120          0       5120   0% /run/lock
tmpfs                                                     2368980          0    2368980   0% /run/shm
/dev/sda2                                                 1922416      35744    1789016   2% /tmp
/dev/sda3                                                 4806140     683960    3878040  15% /usr
/dev/sda6                                                 9612252    1023896    8100076  12% /var
/dev/md0                                               5814368784 1562158184 3959183428  29% /galaxy

Output of parted -l (condensed):
Code:
Disk /dev/sda: 2000GB
Number  Start   End     Size    File system     Name  Flags
 1      17.4kB  2000MB  2000MB  ext4                  boot
 2      2000MB  4000MB  2000MB  ext4
 3      4000MB  9000MB  5000MB  ext4
 4      9000MB  14.0GB  5000MB  ext4
 5      14.0GB  22.0GB  8000MB  linux-swap(v1)
 6      22.0GB  32.0GB  10.0GB  ext4
 7      32.0GB  2000GB  1968GB  ext4            lvm

Disk /dev/sdb: 2000GB
Number  Start  End     Size    Type     File system  Flags
 1      512B   2000GB  2000GB  primary               raid

Disk /dev/sdc: 2000GB
Number  Start  End     Size    Type     File system  Flags
 1      512B   2000GB  2000GB  primary               raid

Disk /dev/sdd: 2000GB
Number  Start  End     Size    Type     File system  Flags
 1      512B   2000GB  2000GB  primary               raid

Disk /dev/md0: 6001GB
Number  Start  End     Size    File system  Flags
 1      0.00B  6001GB  6001GB  ext4

---------- Post updated at 17:36 ---------- Previous update was at 17:13 ----------

I found the problem.

The reason why sda is under heavy stress when using dd on md0(sdb,sdc,sdd) is the swap.
Code:
for i in {1..10}; do
  dd if=/dev/zero of=$(mktemp /galaxy/XXXXXXX) bs=1G count=1 &
done

Using 10 times dd with bs=1G require 10G memory which I don't have. So the system uses the swap on sda and md0 is quietly waiting doing nothing.

Code:
for i in {1..10}; do
  dd if=/dev/zero of=$(mktemp /galaxy/XXXXXXX) bs=256M count=4 &
done

Using 10 times dd with bs=256M require 2.5G memory which I have. So all the stress is on md0.
 
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