Isilon Connection Notes for OSX Clients

Notes for Mac OSX clients

 

CNAME Use

Since OSX doesn't currently support DFS namespaces, we offer a CNAME that points to the cluster's current location. This is of particular use for Gold instances in case of a Disaster Recovery incident - the replicated filesystem will be rolled over to the other cluster (in SSRB or UFDC, depending on where your initial filesystem is located). For the silver or bronze replication, using the CNAME is optional - you could use the location specific DNS name for the server name in your path instead. 

 

DEVICE vs SHARED

The Isilon cluster has its own DNS server running on it. When the client issues a request to connect to the file share, it issues the ip address for one of the cluster nodes, typically based on lowest activity. OSX's connection caching software can apparently experience an issue connecting to the same file share name using multiple ip addresses returned.  

If you haven't used the attached filesystem in a while and click on the SHARED entry for the server in the Finder sidebar to refer to an Isilon fileshare, the client will issue another connection request, which can result in getting a new ip for the server. This will sometimes result in no shares being listed for the server in Finder. 

More odd is that the client will sometimes try to reauthenticate to the server as "Guest", which is disabled. This will result in a failed connection attempt and the server will display in Finder as "Disconnected".

If you run the mount command from a terminal window, you will see multiple mounts for the same filesystem with different names resulting from the connection attempt to a different ip address for the same resource. Each mount will display a share name followed by a number (-1, -2, etc).

A workaround for this issue is to use the DEVICES entry in the Finder sidebar rather than "SHARED". Isilon's recommendation is to go into Preferences for the Finder and uncheck the box next to "Connected Servers" under "SHARED" to remove the connected server from view altogether.

If your Finder does not display DEVICES in the sidebar in Finder (it will typically be an icon for your computer) dragging the mounted server volume into the sidebar of the Finder window will cause DEVICES to display.

 

Performance considerations

Because of support implemented for a TCP algorithm called the Nagle algorithm, performance from Samba based filesystems can be slower in general for OSX clients. There's a system configuration entry that can greatly improve performance for OSX clients if this proves to be a problem.

Add the following setting to /etc/sysctl.conf (you will need to use a unix-type editor like nano or vi to do this):

 net.inet.tcp.delayed_ack=0

You will need to restart the computer for that setting to take effect. 

This setting causes the tcp stack to respond with an acknowledgement after every packet is received at the expense of additional cpu cycles. Another alterative is to set the delayed_ack to the number 2, (called "compatability mode") which responds with an acknowledgement after every other packet. 

The default setting in OSX is equivalent to mode 3, which means that the client will automatically detect when to send the acknowledgement, typically waiting for 4 packets to be received before responding. 

The issue caused by the Nagle algorithm manifests itself when an odd number of packets are received by the client - it causes a delay acknowledging them because the client is waiting for one more packet to be received before doing so. This causes the client to wait for a timeout period before responding.