Re: Thoughts on xServe RAID replacement?

Craig,

There are a number of factors that need to be considered when when selecting the appropriate type of storage and/or storage data interface. Obviously, price is going to play a big part in it but performance, ease of integration/management and potential for future expansion are also going to have an important place in the final decision process. Ultimately, you will need to find a "comfortable" balance between these for your particular environment.

Deciding between an "internal" RAID (external JBOD storage array with an plug-in RAID controller in your server) and a purely external solution (RAID controller built-in to the storage array) is a little subjective. A JBOD array is definitely cheaper than an external RAID system; however, you will also need to factor in the cost of the internal RAID controller to get a true comparison. However, a JBOD solution is completely dependent on the workstation/server so a failure there could be disastrous for your stored data. An external RAID is completely independent and "agnostic" of the host computer so data is a little more secure and you could even swap out the entire host system without affecting the storage. Expansion is also typically more common with external RAID systems. Finally, integration is definitely easier with an external RAID system; JBOD systems require the integration of internal hardware, loading and configuration of appropriate drivers, etc.

The type of data interface will largely be driven by your performance requirements, although ease and convenience of integration will also play a part. For the most part, there are 3 predominant interface types that you can choose from; Fiber-Channel, iSCSI or SAS (for internal systems SAS is really your only option). iSCSI is, without doubt, the easiest to integrate as it simply plugs into one or more of the existing LAN ports on your computer. However, most iSCSI RAID systems are limited to GbE so performance will only be about 70MB/s. You can increase this by "bonding" multiple ports (link aggregation) but this would require a storage system that supports multiple data ports (such as our RS series) and may require the addition of a multi-port NIC to your server.

At the other end of the spectrum is the SAS interface. By far, SAS will give your the best data throughput potential of all of the available interfaces. However, you will need to add a SAS interface to your workstation/server so you'll have to add that cost to the overall price of the solution. Maximum cable lengths for SAS are also a lot shorter than either GbE or FC, so that may be a factor.

Finally, Fibre-Channel (FC) stands somewhere between the other two interfaces. FC is definitely faster than GbE but is nowhere near as fast as SAS. FC also shares the extreme cable length capabilities of GbE but does require fairly expensive interface hardware to be added to you computer. In your case, however, you already have an FC controller in your server so that could make a fibre-channel solution a viable alternative for you.

If you need to get more information on any of the ProAVIO products, you can find full information on the Enhance Technology (http://www.enhance-tech.com) web site (Enhance is our parent company).

Thanks.

Stephen Davies
Technical Sales Representative
PROAVIO USA