IOPS

Input (read) and ouput (write) per second.

noatime into /etc/fstab

when you stat a file you can see four different time tracked:

  • atime (last access time)
  • mtime (last modify time: content change)
  • ctime (last change time: linux permissions, disk location, …)
  • birth time

To improve performance you can specify not to update atime on a directory or a file via the fstab option noatime, for instance:

# /etc/fstab content example:
/dev/sda1   /data   ext4   defaults,noatime   0   2

By default, the option activated is ‘relatime’ (since linux kernel 2.6.30, before it was atime), it’s a compromise between atime and noatime

The noatime option mustn’t be used if you use some software that are based on the last access time (atime), and that is the reason why relatime was created in order to improve performance and ensure all applications still be valid.

How calculate IOPS?

if you have a disk capable of writing 155 MB/s with 4k blocks (4096 Bytes):

155 * 1024 * 1024 / 4096 = 39680 IOPS

inversely if you have disk capacity of 40k IOPS (40000 IOPS) and disk blocks size are 4k (4096 Bytes):

40000 * 4096 / 1024 / 1024 = 156,25 MB/s