Tuesday, April 1, 2008

Drobo v. ReadyNAS III: Connectivity and use of drives

Previous posts have addressed by needs/criteria and some of the obvious differences between ReadyNAS and Drobo. This time, I'm getting a bit more technical. 

Drobo does not do Ethernet by itself. That means that it is not a truly a "network attached storage" device. However, DroboShare is designed to work with Drobo to put it on a network. There are some advantages and disadvantages to this setup. 
  1. If you want to connect it to your computer by USB, you have that option, unlike with ReadyNAS (RN). You can even switch it up from time to time, without impacting your data.
  2. If you know that you don't need an Ethernet connection, you don't even need DroboShare, and can save the $200. 
  3. USB 2.0 is not the fastest way to connect a drive to a computer, FireWire is. Moreover, gigabit Ethernet can be faster than USB. Drobo is stuck with that USB bottleneck on speed, because it connects to DroboShare with USB.
However, my router -- Apple AirPort Extreme BaseStation -- can share USB drives plugged into its USB port. Therefore, I don't need DroboShare. Because my computers access the network wirelessly --being laptops -- USB is not the bottleneck. Rather, the slower speed of wireless networking is the bottleneck.  The only times that I might be able to take advantage of ReadyNAS's real speed advantage (i.e. gigabit Ethernet) would be when I plugged a network cable into my laptops. And to do that, I'd have to replace my router and the hub in my office with new gigabit equipment. For me, ReadyNAS's faster connections just don't matter. 

The second big technical difference is how each device handles expandability. This expandability is the coolest thing about each of them. When they close to full, you can add more drives until they are full. If you are already using all four drive bays, you can replace the smallest drive with a larger drive and get more space. Yes, they each  can use drives of varying sizes simultaneously! This means that you can just by the most cost effective drive -- by which I mean the least $/GB -- at the time. Later, when you need more space and storage prices have dropped further, you can buy another larger disk. They both grow as you grow, and each allows you to take advantage of the fact that larger drives become available every few months and the cost per GB keeps going down. 

However, there are some differences in how they handle disks of difference sizes.

ReadyNAS treats every drive as though it is the size of the smallest drive. This means that the extra space on the larger drives are ignored. When you replace the smallest drive with a larger drive, ReadyNAS will then use more space on every drive. For example, if it has four different drives - 100GB, 200GB, 300GB, 400GB -- it only uses 100GB on each disk. If you replace the smallest disk, say with a 500GB disk, it then checks what the new smallest disk is (in this case, 200GB), and only uses that much space on each drive. It's a very simply approach. If you have larger disks, it doesn't use that space now, but will use it later when other disks catch up. 

Drobo also ignores some space, but far less. Rather than ignoring space on all the drives, it just ignores space on the single largest drive. It ignores the extra space on the largest drive in excess of the size of the second largest drive. So, in the previous example, it ignores 100GB, because 400GB - 300GB = 100GB. Unless the three smallest drives are the same size -- and the fourth can be the same size or larger -- Drobo ignores less space than ReadyNAS, and it never ignores more space. 

Both devices essentially use one drive for redundancy, so that if anything happens to any of the drives you data is still safe. For Drobo, the spaced used for redundancy and the space ignored add up to the capacity of the largest drive. With ReadyNAS, it's a bit more complicated, but always more than than.

So, here's how it works out for each device in various configurations. 

Example 1: 
Drives: 100Gb, 200GB, 300GB, 400GB
           ReadyNas Drobo
Available   300GB   600GB 
Redundancy  100GB   300GB
Ignored     300GB   100GB

Example 2: Replace the smallest drive above (100gb) with a 500GB drive.
Drives: 200Gb, 300GB, 400GB & 500GB
           ReadyNas Drobo
Available   600GB   900GB 
Redundancy  200GB   400GB
Ignored     600GB   100GB

Example 3: Start with the most cost efficient drives available today, and add larger drives later.
Drives: 750GB, 1000GB, 1250GB & 1500GB
           ReadyNas Drobo
Available  2250GB   3000GB 
Redundancy  750GB   1250GB
Not used   1500GB    250GB

Almost regardless of your configuration, Drobo uses more of the drives' capacity. This means that, in addition costing less upfront, it will cost less over time for a given amount of available storage. Or, you'll get more storage for the same amount of money. And once you have filled all four drive bays, regardless of your configuration, if you replace your smallest drive with a larger drive you will get more space. Whereas with ReadyNAS, if your smallest drive is not the only drive that size (i.e. you have another drive the same size as your smallest drive, or even all four drives are the same size), you have to replace multiple drive to get more usable space.

Clearly, advantage Drobo. 

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