Re: How does the hrStorageTable handle very large disks (> 20tb, for instance).

On 29 February 2012 16:59, Day, Robert <[email protected]> wrote:
> I’ve been dealing with this problem for some time.  We have some large disks
> here that cannot be measured accurately in the hrStorageTable due to a 32
> bit integer being too small.

That's not strictly true.

The hrStorageTable uses two column objects to represent the size
of a disk partition (or other storage element) - hrStorageSize and
hrStorageAllocationUnits.   Both of these are 32-bit values, but in
combination can handle elements up to 2^64   (16 exabytes)

If hrStorageAllocationUnits is fixed at 1 (i.e. individual bytes),
or 1024 (i.e. measured in K), then this will limit hrStorageSize
and similar to 2^32 = 2 Gb or 2^42 = 2 Tb respectively.
   But the hrStorageTable can handle larger disks quite happily,
and more recent versions of the Net-SNMP agent are starting to
take advantage of this.


>  I understand that when the value is too large,
> it raps the counter.

That is true of counter-based objects - but that's not really relevant
here.   The only counters in the Host Resources MIB are two error
counters (hrStorageAllocationFailures and hrDeviceErrors).
   The size metrics are simple Integer values - probably the most
sensible behaviour on overflow would be to latch at the maximum
value.   (See the description of Gauge objects in SMI)

>   Does net-snmp have any mib available similar to the
> hrStorageTable that shows disk logical disk information with 64 bit
> counters?

a)  Forget about counters - they're not relevant here

b)  The hrStorageTable can already handle larger disks - see above

c)  The Net-SNMP specific 'dskTable' has entries which *are* limited
       to 2Tb   (i.e. 32-bit values, measured in Kb)
    namely dskTotal, dskAvail and dskUsed.

    However these are accompanied by equivalent "paired" objects
     dskTotal{High,Low}, dskAvail{High,Low} and dskUsed{High,Low}
    which provide 64-bit representations (again measured in Kb),
    and so will handle disks up to 2 Zettabytes.
         That should be sufficient for the forseeable future!

Dave

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