One of the good things about selecting storage technologies today is that there are plenty of options. Further, many storage systems don’t use the traditional RAID 1, RAID 5 and RAID 6 offerings. There are a few RAID technologies that are proprietary to a particular storage product. Two that come to my mind are NetApp’s RAID-DP which is loosely analogous to RAID 6 and Drobo’s BeyondRAID.
Recently in a few situations I have started working with the NETGEAR ReadyNAS series of unified storage products. Note the unified distinction, which means it can provide both file (CIFS, HTTP, NFS, FTP and more) storage as well as block storage via iSCSI. The ReadyNAS series provides the X-RAID2 disk protection mechanism. X-RAID2 is loosely equivalent to RAID 5 in terms of protection overhead, but it does have a few differentiating features.
First of all, X-RAID2 does not deliver a fixed-size logical unit. So, let’s take an array of three hard drives that are 750 GB each. This would present over 1 TB of usable storage space for all of the block and file storage protocols to consume from. But, what is cool about X-RAID2 as implemented on the ReadyNAS series is that you can add additional drives that are larger and both the usable storage pool will expand and the volume that started with 3 drives can be expanded to use the larger drives. Once this happens, a restriping technique is used. Below is an example I was working with — Figure A shows a volume that had five hard drives while it is being restriped to include the newly arrived sixth hard drive:
Click to enlarge.
Depending on the model, the ability to leverage large drives depends on available slots. This may be avoided with intentional failing out of a drive to restripe to a larger drive, however.
Leveraging disk technologies that can work with drives of dissimilar geometry may be a very welcome step given the recent shortage of hard drives and the associated increase in storage costs.
Have you used X-RAID2 much? I’ve used it in a few virtualization scenarios and have been very happy with it for the class of storage I’m using. Share your comments below.