Thursday, July 2, 2009

Server “Wake on LAN” technology enables Xiotech’s PowerNap energy efficiency feature.

With their recent announcement of PowerNAP™, Xiotech joined the ranks of storage vendors offering energy efficient storage. Although currently restricted to the Emprise 5000 I suspect that it will permeate upwards in the not to distant future.PowerNAP™ is an uncomplicated approach to energy efficiency. Storage arrays are powered down based on a predetermined schedule. Think of storage in a remote office with well defined hours of business, a back-up or DR target or an inactive archive data repository. These use cases all have predictable time when the hosted data is unlikely to be requested and instead of simply allowing the inactive disks to continuously and unproductively spin, the subsystem is powered down.Wake on Lan originated in the server world; simply put it activates sleeping devices by sending out what is called a Magic Packet, a broadcast frame that contains a 6 bytes of 1’s followed by 16 repetitions of the target devices MAC address. As some organizations may not permit broadcasting or unicasting packets across a LAN it may take some “buddying-up” by the storage folks to their networking compadries to get the required support.This approach is not as dynamic as some other power management features where it is the activity profile of the data that determines the power state of the drives. While WOL can respond to unpredictable circumstances and wake the drives up, out of sequence power down required a manual intervention.How much of a negative is this approach. I guess it depends. If workloads are highly predictable, as per the examples above then this approach should work fine. However this is an all or nothing approach with the array powered up or powered down. It lacks the granularity or flexibility to optimize energy efficiency in systems that host a broad spectrum of active and inactive data. Automating the process is via scripts and while not particularly onerous its ease of use falls short of competitive GUI driven management. Admittedly my impressions are based on documentation and not hands experience but not automating data and device integrity checking is questionable at best.On the plus side when the system is powered down only consumes 1W, impressive! On power down all I/O’s in progress are completed and the cache is flushed prior to shut down. On receiving a WOL request the array is up and ready to service data after an acceptable 60 second delay.Xiotech are not alone in using the WOL approach for storage solutions. At SNW I looked at the NAS boxes from Netgear. These compact 1.5TB to 6TB storage units targeted at SMB, professional office or even the power geek’s home installation.

No comments: