RAID Advice

[Simon Frances]

Hi,

I have a Mac Pro and a Sonnet Fusion 500P RAID enclosure, the RAID has 5x 500GB drives and the Mac Pro has 4x 500GB drives. I would like some recommendations on how best to configure my system; firstly, whether or not to RAID the drives in the Mac Pro and if so, all four or a selected few, i.e. should the system drive be RAIDed or not?

What should the block size be set to, both for the Sonnet and the Mac Pro?

I’ll be primarily using the Sonnet for video editing (FCP) although I’ll be using it for other general stuff including Photos, Photoshop etc... As for the Mac Pro, general stuff.

Regards,
Simon

[Robert Lane]

Simon,

eSATA RAID's such as the Sonnet Fusion have more than one way to connect to the system, either JBOD, Port Multiplier or Infiniband. Which HBA or controller card did you get to connect to the Fusion?

The best method for eSATA is either JBOD where each drive get's it's own eSATA cable or, Infiniband which is similar but the connecting cables are actually bundled together into a single connector.

The *worst* method of eSATA connectivity is PM or port-multiplier. This forces the data of all drives into a single cable thereby creating a bottle-neck of dataflow. Don't believe the glossy ad campaigns about PM devices, they simply cannot perform as fast as JBOD or I.B.

To answer your question, you will not see very fast performance figures by setting up an internal RAID in the Mac Pro; you're best off leaving those drives as singles. Depending on which HBA you have you can setup one of several RAID externally in the Fusion, but which one to use is best decided by your backup strategy and whether or not you want redundancy or massive storage/speed.

eSATA arrays are best suited to RAID-0 mainly because they cannot hold the same data rate while working - they slow down as you use them - because there is no controller cache to offload the HDD cache filling up.

Setting up a RAID and understanding the implications is not simple and I'd suggest getting with one of the forum sponsors in your area to get some training.

[Simon Frances]

Hi Robert,

Thanks for your reply.

I’m connecting the Fusion to a Tempo SATA E4P via an eSATA data cable and using the Port Multiplier method.

On the back of the Fusion 500P, you can only connect one cable to it. Is there a way to connect this system via the Infiniband route as you suggest? Not to quote you but I’m looking for massive storage/speed.

Thanks again,

Simon

[Robert Lane]

PM is the worst performing of all eSATA connections. If possible, I would exchange the 500 for the 400 which uses a single, eSATA cable for each drive. Although you won't have as much storage available you'll almost double your throughput speed - initially.

If you've had the unit too long and Sonnet or whomever you purchased the unit from won't return it, there's nothing you can do to change the connection type because it's built into the backplane of the Fusion box and Sonnet doesn't make an Infiniband connector for that box.

So if you're stuck using the 500 the best thing you can do is a RAID-0 using Disc Utility and make sure under the "options" tab for block size you select 256k. That will help the built-in drive cache work a little smoother, but as I mentioned before the array *will* slow down as you use it because the E4P card does not have any on-board cache to offload the HDD caches when they fill up.