Red Hat Bugzilla – Bug 1286282
dmstats: support non-dm devices for stats create
Last modified: 2017-07-19 08:02:46 EDT
Description of problem:
Device-mapper IO statistics can be used with any block device providing a dm-linear layer is mapped over the underlying device, e.g.:
# dmsetup create sda --table="0 2048 linear 8:0"
# dmstats create sda
# < ... do stuff ... >
# dmstats delete sda
# dmsetup remove sda
Doing so is tedious and requires the user to have knowledge of device-mapper targets and table syntax.
By providing the ability to automatically create the linear map when required (and when the requested device is idle) the use of device-mapper statistics with non device-mapper devices is considerably simplified.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. dmstats create /dev/sda
# dmstats create /dev/sda
Device sda not found
* creates dm device "sda"
* registers requested stats regions on dm device "sda"
Hmm, while I can understand motivation IMHO it's better for a user to 'convert' to lvm2 - it might not obvious on the first sight but in fact you would need to provide 'stacked' device from 'boot' moment.
IMHO we could probably make it more easier is to add capability to switch any device into lvm2 device - there is in fact lot's of 'hidden' code in lvm2 to actually support this - but it's awkward to use.
While there could be some 'use' for 'unused' devices - so before the use the user can use 'linear' mapping instead of real device, but there are still lots of 'security' issue connected to this - so IMHO such solution could be only seen as a temporary hack to do things in quick but highly unsecure way.
lvm2 would be a separate request - outside the scope of this bugzilla
*** Bug 1286283 has been marked as a duplicate of this bug. ***
Moving feature request from RHEL to upstream.
Added dmstats subcomponent
Might be clearer to start by providing a command that just wraps a linear mapping around a given device, subject to certain conditions. We might also be able to build this into the boot process as a substitute for the original device.