X-RAID — RAID for the rest of us

April 18, 2008 by  
Filed under Uncategorized

Perhaps you may have never heard about X-RAID™ until you started looking at the ReadyNAS. That’s because X-RAID is a NETGEAR patent-pending technology that is available only on the ReadyNAS. And it’s a proven technology that has been shipping in volume since 2004.

What is X-RAID you may ask? Well, let’s take a look…

First of, RAID if you are unaware stands for Redundant Array of Independent Disks, simply a way of protecting your data in case of a disk failure. The X in X-RAID stands for “expandable”, and as you may guessed, X-RAID is expandable RAID. So you’re probably asking “great, it’s expandable, but how?” or “how much work do I need to make my RAID expand?”

The answer is it’s automatic. That means there’s no need to worry about selecting the wrong command or trying to remember the right series of steps. The ReadyNAS makes all the right decisions for you.

To really see how easily it works, let’s start out with a one-disk ReadyNAS and go through the X-RAID expansion process. Remember that with just one disk, there’s no data redundancy, so when that one disk fails, your data is lost.

1disk.jpg

Adding a 2nd disk

If you had started off with a one-disk ReadyNAS and wanted to have protection from disk failure (often referred to as having redundancy), you’ll need to add a 2nd disk that is at least as large as the first disk. The disk can be added when the ReadyNAS is powered off, or it can be hot-added while the ReadyNAS is running. Simply insert the disk into an empty tray, secure it with 4 screws, and insert the tray into the a disk slot. It can be any slot, but to keep it simple, add it to the 2nd slot from the left.

Once the 2nd disk is added (or when the ReadyNAS is powered on after adding), your 2nd disk will start syncing to the 1st disk. Depending on the size of your disk, it may take anywhere from 30 minutes to several hours. The sync occurs in the background so you can still keep on working with the ReadyNAS during this time.

2disk.jpg

Once the sync process completes, your data volume is now redundant, meaning if one of the disks fails, the other disk still contains the data, and thus your data is now fully protected from a disk failure. The capacity of the disk is the same as when you had just one disk.

Adding a 3rd disk

You can add the 3rd disk just like you added the 2nd disk. For our discussion, we’ll hot-add the disk, as you really don’t need to power-down the ReadyNAS if it supports hot-swappable disk trays. Just make sure you are adding a disk of at least the size of the 1st disk. You can add a larger disk, but the extra space will not be utilized until all disks are at least that size.

Once you’ve added the 3rd disk, the disk will be initialized and will be scanned to make sure it is good. This is done in the background and can take anywhere from 30 minutes to several hours, again depending on the disk capacity. There’s no performance impact during this time and you can continue to work with the ReadyNAS during this init process.

When the init is complete, your data volume will begin to expand automatically. Again, this is done online, so you can continue to work while the expansion is going on. The time for expansion depends not only on the disk size but also the number of files in your volume. The more full and the more files you have in your volume, the longer the expansion process. Typically the expansion process can take an hour to 12 hours or more. Once complete, your existing data will still be there, but your data volume will be twice the size of your 1st disk, and it remains protected from a disk failure.

3disk.jpg

One thing you might notice is that with a 2-disk X-RAID, the overhead for redundancy is one disk, and with a 3-disk X-RAID, the overhead for protection is still only one disk. This will be the case with X-RAID even when you add a 4th disk.

Adding a 4th disk

Adding a 4th disk is identical to adding a 3rd disk, other than the fact that the resulting capacity is 3 times that of the 1st disk. In fact, if you had wanted to add the 3rd and 4th disks at the same time, you can do this to save time. Just add the two disks while the ReadyNAS is powered off, as it’s important to add the two disks at the same time to kick off the init process at the same time.

4disk.jpg

Horizontal vs. Vertical expansion

The process of expanding from one disk to four disks is what we refer to as horizontal expansion. X-RAID also supports another form of expansion that we refer to as vertical.

With horizontal expansion, the capacity is limited to 3x of your original disk. But as larger disks are available or they become more affordable, and you need more capacity, you may want to grow your volume even larger. This is where vertical expansion comes into play.

X-RAID supports replacing each of your disks with larger capacity disks while keeping your data intact, whether you have 2, 3, or 4 disks. Simply replace each of your disks one by one with a larger disk. Each time you replace a disk, the ReadyNAS will initialize it, scanning to make sure the disk is good. This can take anywhere from 30 minutes to several hours, just like in the horizontal expansion process. After the init process, the disk will be sync’d to restore data redundancy. Again, this process can take 30 minutes to several hours. Both these processes occur in the background, so you can continue using the ReadyNAS as usual.

vertical.jpg

Once you have done this for all four disks, just reboot the ReadyNAS to start the volume expansion which occurs in the background. When the process completes, your data will remain intact, but your data volume capacity will have expanded to 3x of the smallest capacity disk in your ReadyNAS.

The beauty with vertical expansion is that you can keep expanding your volume repeatedly with larger capacity disks, a definite future-proof advantage that you can count on with the ReadyNAS.

Comments are closed.