Oracle ZFS Storage Appliance: 'unknown' file names under the Analytics display output

Asset ID:	1-72-2191897.1
Update Date:	2018-01-05
Keywords:

Solution Type Problem Resolution Sure

Solution 2191897.1 : Oracle ZFS Storage Appliance: 'unknown' file names under the Analytics display output

Applies to:

Sun ZFS Storage 7420 - Version All Versions to All Versions [Release All Releases]
Oracle ZFS Storage ZS3-BA - Version All Versions to All Versions [Release All Releases]
Oracle ZFS Storage ZS3-4 - Version All Versions to All Versions [Release All Releases]
Sun ZFS Storage 7120 - Version All Versions to All Versions [Release All Releases]
Sun ZFS Storage 7320 - Version All Versions to All Versions [Release All Releases]
7000 Appliance OS (Fishworks)

Symptoms

Using analytics can really help to frame the ZFS appliance activity/performance . The focus can be toward shares and even each filename of the shares.
We can use, for example, the following analytic : NFSv3 operations per seconds broken down by filename.
Unfortunately, most of the activity may be reported against <unknown> file names.

Capture of analytics

The "Sun ZFS Storage 7000 Analytics Guide" tells this :

There are some circumstances where the filename is not known, such as after a cluster failover and when clients continue to operate on NFS filehandles without issuing an open to identify the filename.
In these situations the filename reported is "<unknown>".

Actually, this is not the only case.

Changes

This behavior has been present since the very first release of the ZFS Storage Appliance in 2008.

Cause

The key is that NFS is able to read/write into a file without keeping it open.
Systems or applications like Databases, dNFS or Vmware do not need regular lookup to keep using their files.
So initially, the vnode (virtual node) has the path set and Analytics is able to display it.
The vnode is also stored in the DNLC (Directory Name Lookup Cache). But without lookups or open, the vnode is not referenced and can eventually be evicted from the DNLC.
The ZFS ARC object that holds the vnode can then be evicted from memory and that's when we start seeing <unknown>.

Solution

From the client side, a simple lookup (ls) on the file, issued from the client is enough to recreate the information inside the ZFSSA allowing Analytics to continue displaying the data until the next eviction.
If a directory is suspected, a UNIX command such as find in the directory will help to get the DNLC re-populated with filename entries.

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