On 02/14/2017 03:43 PM, Tim Small wrote:

Hello,

A design question for a user-space RAID monitoring tool.  The tool is
intended to export machine-readable md state so that the system owners
can creating automated alert policies etc.

Should it get its information on md device state from /proc/mdstat, or
/sys/block/*/md/ as a data source, or should it use the ioctl interface
that mdadm uses (on the basis that this is more complete / heavily tested).

I assume the issues are:

. usability (/proc/mdstat is intended to be human-readable so machine
parsing it seems bleugh - it's also incomplete?)

Yes.

. stability (perhaps /sys/block/*/md/ is less stable than the ioctl or
proc interface?  Or perhaps it's just fine and won't break in
backward-incompatible ways?).

I'm not sure if there are any guarantees here; we _try_ to keep the
sysfs interface stable, but ...

Any thoughts?

Should I see which way the recent "add bad block flag to disk state"
patch-set thread goes?

Hehe.

Unfortunately the only tool able to provide a consistent view of the MD
RAID status is called 'mdadm'.

Problem is that you each of the various interfaces (ioctl, /proc/mdstat,
/sys/block/*/md) provides you with different information. So your
userspace tool would need to parse all of these information sources to
get a consistent view.

I did a similar thing myself for my md_monitor program
(github.com:/hreinecke/md_monitor.git), so you could have a look there
for some further information.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)