X marks the sweet SAN spot
Apple Xsan offers industrial-strength performance and stability at a low, low priceFollow @infoworld
In the mid-1980s, Apple took its first steps into the corporate technology market and stumbled so badly that it was more than a dozen years before the wounds could heal. In the past few years, however, the company has made significant strides toward becoming a player in enterprise computing: Apple’s rack-mount Xserve server and Xserve RAID array chassis can hold their own with anything in their class.
It’s taken until now, though, for the software to catch up with the hardware. In particular, sharing data volumes across OS platforms required administrators to use the Samba SMB implementation (ick) or NFS (double-ick). Fortunately, those are no longer the only options available, with Apple’s introduction of Xsan, which allows administrators to build SANs on what passes for the cheap.
At its simplest, Xsan is a port of the StorNext File System from Advanced Digital Information Corporation (ADIC) that sells for significantly less than the equivalent bits for Linux, Unix, and Windows systems. Apple’s base price is $999 per connected Mac OS X machine, whereas StorNext FX clients -- which ADIC markets for Xsan environments -- cost up to three times as much: $1,750 for Linux and Windows, and $3,000 for other Unix platforms.
This “simple port” doesn’t include any tools for managing the data itself, at least not in the way one might expect in a SAN environment, where terabytes of data are slung around. In particular, lifecycle management is left to ADIC’s own StorNext Storage Manager or similar products. But Xsan beats all comers in the game Apple knows best: adding an attractive and intuitive interface to powerful software.
A Winning Point
The first release of Xsan came out in early 2005. After using it in the lab for several weeks, it became clear to me that Xsan 1.0 wasn’t review worthy. That changed at the solstice, with the release of Xsan 1.1 and Mac OS X 10.4. Xsan 1.1 delivered a notable improvement in the stability of the SAN, and the OS upgrade expanded the maximum supported volume to 2 petabytes. Although upgrading my test bed was no picnic, I thankfully didn’t have to reformat any volumes in the process.
As recommended, I used the Xsan Admin tool to create storage pools to aggregate LUNs (logical unit numbers) of similar properties, and then to create volumes out of storage pools. In my case, I chose to create two single-pool volumes on my smaller Xserve RAID units, and a striped dual-pool volume on a 5TB Xserve RAID. Xsan can’t mirror LUNs or pools.
Xsan Admin also manages access control, monitoring, and notification; Apple’s RAID Admin tool and Fibre Channel Utility take care of lower-level processes. Xsan Admin relies upon Apple’s Open Directory implementation of LDAP to supply user and group information for Mac OS X clients, so Xsan MDCs can consume supported foreign directories, including Microsoft’s Active Directory.
SAN administrators will find, however, that their most frequent task in Xsan Admin will be mounting and unmounting volumes on Mac OS X clients; one can also monitor how long volumes have been mounted on each client. Because stability was such a problem in Xsan 1.0, I kept a close eye on that figure when testing Version 1.1; I finally stopped counting after two weeks. Unfortunately, the management is volume-by-volume; one can’t see at a glance to which volumes a given client is connected.