We noticed some performance issues on one of our Netapp Filers and during my investigation I noticed a few things that happen under the covers and I wanted to share them with you.

Netapp SnapMirror is an asynchronous method of mirroring files from one location to another. At my company we use it to replicate property images from one datacentre to another. I've always wondered what happens to the replica as SnapMirror is a block copy though obviously the destination may be different therefore it needs to do something 'smart' to correct the differences between the two filers.

The 'smart'ness is what is causing performance problems - so lets go through them.

Here is some of the output of a 'statit' on the SnapMirror replica. The filer is idle - its not doing any traffic and its not snapmirroring.

nas02*> statit -e

Hostname: nas02 ID: xxxx Memory: 16376 MB
NetApp …

Netapp, enterprise network attached storage devices with OS, Data ONTAP has a per volume specific variable called 'maxfiles'. Basically the maximum number of inodes the volume can consume independent of disk utilization.

Unfortunately this variable must be set per volume, it cannot be 'unlimited' and it cannot be downsized.

According to the man page:

DESCRIPTION
maxfiles increases the number of files that a volume can
hold, as close as possible to max. File inodes are stored
in blocks, and the filer may round the requested max num-
ber of files to the nearest block.

Once increased, the value of max can never be lowered, so
the new value must be larger than the current value.



Further increasing this value to be an unlimited-like variable consumes filer RAM and will result in less usable filer RAM after a Data ONTAP OS …