diskio: ability to report only devices, not partitions

[randallt]

Feature Request

Proposal:

Easily filter partitions from being reported.

Current behavior:

Have to use the "devices = [ ... ]" mechanism to try to filter out partitions, such as
devices = [ "sd?" ]
to only get sda, sdb, etc., without getting sda1, sda2, etc. However, if my device naming changes, this will no longer apply.

Desired behavior:

Can easily ignore partitions lines by specifying
ignore_partitions = true
or equivalent. A way to do this on linux is to only match devices with a minor number zero in /proc/diskstats.

Use case: [Why is this important (helps with prioritizing requests)]

We use system images that have several devices and partitions. For the diskio plugin, this is way too chatty. We would like to only report on the devices, without having to guess at a device naming convention.

[danielnelson]

I'm not sure the minor number being 0 would work in all cases, on my system the first device mapper partition also matches:

   8       0 sda 355695 852 14086167 101987 2849736 1451871 128171168 3720277 0 1150248 3819033
   8       1 sda1 175 0 15104 40 0 0 0 0 0 36 40
   8       2 sda2 354900 852 14058879 101846 2302331 1451871 128171168 3178906 0 791621 3277655
 253       0 dm-0 355762 0 14052208 182310 4305343 0 128171168 35355967 0 1521174 35551163
 253       1 dm-1 174838 0 5459754 65744 1241146 0 19664928 13787844 0 460953 13871589
 253       2 dm-2 45 0 2336 24 0 0 0 0 0 16 24
 253       3 dm-3 152252 0 3033274 58118 2003500 0 86875136 19821232 0 531269 19880477
 253       4 dm-4 9035 0 3562490 45286 12231 0 1465880 121756 0 51714 167056
 253       5 dm-5 19501 0 1988690 13627 672278 0 20165224 1462586 0 501966 1476553

I wouldn't want to just move the guessing into the plugin, but perhaps we should add major/minor number to the tagset?

[danielnelson]

I guess dm-0 is the full device mapper, but I still am unsure if this is always a valid way to determine the full disk.

[randallt]

Ah. Looks like you are right. Unfortunate. I see dm-0 as just another device--it is not cumulative for the others. Any other possible way to do this?

[danielnelson]

Perhaps this heuristic will work well enough in your environment. What if we add major/minor as tags:

diskio,name=sda,major=8,minor=0 value=42

And then you can use tagpass/tagdrop to filter:

[[inputs.diskio]]
  # ... snip ...
  [inputs.diskio.tagpass]
    minor = "0"

[randallt]

No, I think you are right that major/minor doesn't work well enough for this. I would need those dm-* devices as well. I'm fine to close this as unworkable if there's no other way.

[danielnelson]

Maybe this could work?:

[[inputs.diskio]]
  device_tags = ["ID_PART_ENTRY_NUMBER"]
  [inputs.diskio.tagdrop]
    ID_PART_ENTRY_NUMBER = "*"

[randallt]

You forgot the brackets:
...
device_tags = ["ID_PART_ENTRY_NUMBER"]
[inputs.diskio.tagdrop]
ID_PART_ENTRY_NUMBER = [ "*" ]

It doesn't work without them, but it does work with them, at least on my test system (Centos7 VM). Question is, can we shortcut this with a single config option?

[danielnelson]

I believe we would want a cross platform way of doing this first, which might be challenging, but also I would want to see how much demand exists for an option like this.

[randallt]

Hmm, on second thought, it looks like we would want to exclude the device mapper, and just get metrics on the underlying devices.

[danielnelson]

Can you add name = ["dm*"] to the tagdrop table?

[sspaink]

Closing as there hasn't been any activity for quite sometime, if anyone is still interested in this please re-open or leave a comment. Thank you!