Doorways in and out

Xsan Xamination – 3

This is the third part of our Apple Xsan examination.

Going outside the garden wall

By adding a Windows or Linux server running the Quantum-sourced StorNext FX product non-Mac OS X clients can be added to the Xsan network of accessing systems. For example, Windows client systems with FC HBAs and a FC link to the Xsan switch can access Xsan volumes. The StorNext server acts as a translation facility mapping their file access calls to and from Xsan calls.

The reverse is true. Mac and Xserve clients with Xsan can be added to an existing StorNext SAN environment via an intervening Windows or Linux box running StorNext.

By running the StorNext Management Suite on a Windows or Linux server, plus a Quantum (ADIC) metadata controller FC-linked to the Xsan switch, a Quantum Scalar tape library can be hooked up to the Xsan switch and disk volumes backed up to tapes in that library.

Also, because this management suite has HSM (hierarchical storage management) facilities, files can be moved from disk to tape as needs specify. The StorNext Management Suite, which includes StorNext FX, is for high-end shops whereas StorNext FX is for just hooking up Windows and Linux clients to an Xsan.

There is no native tape backup in Xsan. Nor is there any replication facility, meaning that the establishment of a remote Xsan for disaster recovery isn’t natively catered for, ecept through the MultiSAN feature.

NAS access, via CIFS for Windows clients and NFS for Unix clients and AFP for non-FC-linked Mac clients, can be provided by hooking up an Xserve, a Mac OS X server, to the switch. It functions as a NAS head in normal SAN parlance. This separate NAS head server is recommended for performance and reliability reasons.

Apple has added user-friendly set-up facilities to Xsan with the Xsan admin assistant. Compared to standard SAN set up procedures these are, literally, a breeze. Apple says they are intended for people who need to use a SAN and not spend their day administering it.

Xsan and StorNext

Back in 2004 Thomas Feil, then EMEA executive director EMEA for ADIC, said: “There is 100 percent compatibility between the Xsan file system and ADIC’s StorNext file system. An Apple Xsan metadata controller and a StorNext metadata controller are functionally the same.”

In other words Xsan is based on ADIC StorNext technology. StorNext 3.0 was introduced in April, 2007. Xsan 2 has diverged from StorNext as a quick overview of the contrast points between Xsan 2 and StorNext 3 shows:-

- StorNext 3 has affinities as does Xsan 2
- Xsan 2 has MultiSAN which StorNext 3 does not
- StorNext 3 has de-duplication and iSCSI support which Xsan 2 doers not.

Apple is developing Xsan technology to suit it and its customers’ concerns and not taking everything that Quantum’s developers put on the table.


Xsan provides NAS-like file sharing to Apple client systems by layering the Xsan file system on top of a virtualised block storage system connected to the clients across a 4Gbit/s Fibre Channel fabric. It is implemented via a metadata controller, a dedicated Mac OS X server linked in to the switch at the heart of the fabric.

This Xsan functions a kind of semi-walled Apple SAN garden with file system capabilities extended to FC-connected Apple client systems.

A second Mac OS X server can be plugged in to the switch and function as a NAS head extending AFP, CIFS and NFS access to Windows, Unix and non-FC-connected Apple clients.

A Linux or Windows server can be hooked up to the switch to enable backing up the Xsan volumes to a Quantum Scalar tape library. It also enables Windows and Unix client systems with FC access to the Xsan switch to access Xsan volumes as if they were Mac clients; it provides a door into the walled garden.

What we have with Xsan is a consolidated storage facility for Apple customers that offers a shared file-based facility biased for media files and away from databases and fine-grained SAN component control with a block-based approach from start to finish.

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