SCSI timeouts on Dell EqualLogic iSCSI SAN Arrays

 VM Squad posted today about a problem he perceives exists with Dell EqualLogic arrays. Its not a problem, but that's what one of competitors is telling people.  The issue is the time it takes to upgrade firmware in our systems, which is 15 seconds in the systems we are selling today. 

What's interesting is that Derek Schwab posted about the exact same thing yesterday and how it worked so well. 

So what's up with that?  

Systems and storage solve intermittent communication problems through SCSI time outs. If the host system can't communicate, it keeps trying patiently for a long time before giving up. This is a lot longer than 15 seconds.  The amount of time depends on the host system implementation, but it is usually more than a minute and can take five or more minutes (or so I'm told). FWIW, this is the same mechanism that is used for multi-pathing.  After a SCSI timeout, the system tries to re-connect using an alternative path.   

So a 15 second delay (not an outage) a few times a year is not a very big deal. If you have to, you can schedule it for non-peak hours. Everything will work, applications will stay up and end users will see a short temporary hang – if they see anything at all. 

About the Author: Marc Farley