Analysis

posted on 14 March 2008 08:29

This is the second part of our Xsan examination.

Note that there is no iSCSI support. An Xsan (screen shot pictured) is a FC SAN and only a FC SAN. Apple's Doug Brooks, server and storage product manager, acknowledged some customer interest in this and said: "It's something we're keeping an eye on. (But) Our media customers want the bandwidth and latency of Fibre Channel. There is an iSCSI initiator for Mac OS X but we haven't tested it."

Today's Ethernet and iSCSI doesn't provide the dependability and reliable fast access of Fibre Channel.  Brooks said: "There are no dropped frames or out-of-order delivery with Fibre Channel."

Tomorrow's FCOE might make Ethernet a viable substitute for Fibre Channel data streams when data centre class Ethernet is a reality.

Quasi-thin provisioning

With Xsan you can apply volumes to different classes of disk and RAID groups: performance-centric SAS drives for fast access; or capacity-centric SATA for reference data storage. We have a rudimentary storage tiering system here.

Storage resources can be expanded on the fly: add new disks; add LUNs; create new volumes; grow volumes almost on the fly with volume growth taking only a few seconds to accomplish. There is no explicit thin provisioning though.

Xsan can have separate volumes hosted on separate metadata controllers. This feature is called MultiSAN and means that logically separate SANs are insulated against each other's failure. You can also copy data from one MultiSAN to another over Fibre Channel with the component SANs not needing to be in the same location. This can be used for disaster recovery.

Xsan also can be told to keep large files stored in a sequential manner for best streaming performance and separating them from smaller audio files or from highly protected files in RAID 1 groups. Through a feature called affinities different classes of storage can be applied to different applications.

Xsan works with LDAP directories to enable user/application access permissions and disk quotas.

Now click here to move on to Doorways in and out.