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The System

  • An instance running on Amazon EC2
  • It is an m1.large EC2 instance
  • The instance is running Ubuntu Server 12.04 LTS

Here's What Happens...

I wanted to measure disk IOPS on my system, and it looked like iostat was the right tool for the job. Please find below sample output from iostat on my system:

user@host:~$ iostat
Linux 3.2.0-61-virtual (host)   05/06/2014      _x86_64_        (2 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           7.26    0.00    1.84    0.23    0.08   90.60

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
xvdap1            6.55        54.12        77.60     618193     886348
xvdb              0.03         0.13         0.00       1477          4

The above seems to give me the information I'm looking for, except it lists a block device that doesn't exist on my system.

If we examine lsblk, we do not find a device named xvdap1:

user@host:~$ lsblk
NAME  MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
xvda1 202:1    0    10G  0 disk /
xvdb  202:16   0   420G  0 disk /mnt

Moreover, xvdap1 cannot be found in /dev/:

user@host:~$ ls /dev/xvd*
/dev/xvda1  /dev/xvdb

I'm inclined to believe that xvdap1 is the same as /dev/xvda1, but why on earth would they have two different names? The two names differ by a single letter p, what does the p mean?

share|improve this question
    
I'd guess it means partition. –  Iain May 6 at 16:34

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