xServe & xRaid Storage Question

The hardware RAID card is for offloading the RAID overhead of the XServe's internal drives to the card. For maximum performance and the ability to use all three drives as one volume in OS X, get it.

The XServe RAID is a standalone unit. By this I mean, it has its own controllers that will manage the RAID set in it. I do not believe it is possible for the drives in the XServe and the XServe RAID to be combined into one volume. By virtue of the XServe RAID being connected via Fibre Channel, I think that will eliminate the two from being combined in any way.

 

I've had first had experince with and xRaid, so i will give you the low down.
Each hard drive in the xRaid is 250Gb drive.

There are two RAID controllers on the xRaid. Each can handle 7 drives (7x250 = 1.75Tb). Each of the RAID controllers can form seperate level 1,3,5 Raid arrays. (I would recomend level 5) If you have equal raid sizes on each controller (ie. 1.75 Tb x 2), you can form a software raid in mac os X for the 3.5Tb.

Now back to you question of creating a RAID with you existing hard drives. The anwser is no. Creating a software RAID is destructive, and devices in the Raid need to be the same size. And I don't think you can software Raid existing Raid.

So if you need 3.5 Tb of storage all on the same vol. Then you are going to need another XRaid with atleast 1.7TB.

Adding drives to the hardware RAID is non-destructive, but from my experince software RAIDing is Destructive. So planing ahead is the best thing as far as software RAIDing is concerned.

 

You can use different size drives in a RAID, the outcome depends on the RAID being used. For RAID 0, they are all summed up. For RAID 1 and 5, it will create a volume using the smallest disk available. For example, say you have a 20GB and two 60GB drives in a RAID 5. It would create a RAID volume with a total capacity of 40GB (20GB across 3 drives). The additional 40GB on each of the 60GB is unused and is therefore a waste.

Some of the newer software RAIDs can be expanded without destruction. I know Veritas Volume Manager enables this for Windows.

As for XServe RAID with two controllers, that configuration stinks if that is required. I would never want to have two hardware RAID volumes combined with a software RAID. It's a shame you can't have one controller create a RAID volume across the entire line of drives and use the other controller as a backup. If someone wants mass storage, this is a much safer and scalable option than having to combine two volumes. I think Apple needs to open some options here like most other SANs do.

 

Forgive me if i am mis-guided, but 14 drives on one RAID controller is a bit much? I remember seeing like 9 or 10 but 14?

 

Not really. I have a SAN at work with 14 drives in it. You should increase the cache on each controller to get more performance, but 14 drives isn't a lot. Take a look at some of those huge EMC boxes. They have hundreds of drives in one volume.

 

but at that point your in the 100k + range?

 

Close.. The SAN infrastructure hit $56k then with drives it came up to about $65k or so. I know, it's not home equipment, but I still think that the xServe RAID's controllers could handle the entire 14 drives, especially since they give you the option of 1GB cache per controller, which is what I have on each of my controllers. Maybe we'll never know..