Last week, I wrote about some of the lessons I learned while implementing Dell’s M1000e blade chassis. A few TechRepublic readers responded and asked me about the SAN side of the equation. This week, I thought I’d take the time to provide some thoughts on the process I went through, why I ultimately chose EMC’s AX4 SAN for my data center, and why I configure my SAN as I do. In particular, I’m responding to this comment left by TechRepublic reader IT Generalist:
“I am also planning on upgrading our data center to a SAN and virtualization type of environment. I’d like to know what other SAN solutions you evaluated from other vendors and what you didn’t like about them. How much were you able to save over other vendors? I am looking into NetApp FAS2000, EMC Celera NS Series/Integrated and Clariion AX4, Dell/Equalogic PS5000XV and HP StorageWorks 2000i MSA. How do you plan on backing up data to a tape drive from your SAN storage? What made you setup dual SAN controllers as Active/Active rather than Active/Passive?”
This is a great series of questions and I’ll take them in order. The first portion asks what solutions I considered. Honestly, I looked across the board. I looked at EMC’s lower-end CX series and even their AX150/150i. I looked at EqualLogic both before and after the Dell acquisition and also at Dell’s own arrays, the NX1950 and the MD3000. NetApp, Compellent, LeftHand and even the JBOD vendor Nexsan all received scrutiny. The list below outlines my reasons for not selecting these options:
- EMC CX: Price. I probably could have purchased a seriously scaled down, limited size array, but that would have been about it. It would have been a start into the SAN game, but I didn’t need the CX series’ scalability and would not have been able to get to serious storage volumes simply because of cost.
- EMC AX150/150i: Scalability. With an upper limit of 10 hosts and a low upper limit on raw storage, I did not feel that the AX150 would scale to the needs of my environment. While I knew I didn’t need the CX’s scalability, I knew that, for my purposes, the AX150 would be a dead end very quickly.
- EqualLogic: Great solution, but pricey. I’m a huge fan of EqualLogic. A few years ago, I purchased and installed a PS200e array in the data center at my old employer. EqualLogic, like some other newer players in the iSCSI market, throws the kitchen sink into their product. Nothing is an add-on; all features are included in the base price. That said, the price of entry into an EqualLogic solution isn’t low, and my budget simply couldn’t afford a reasonably configured array — one with dual controllers and enough raw space to make a difference. If money was not a factor, EqualLogic would have been, if not my final choice, much more seriously considered. By the way, I don’t begrudge the pricing on EqualLogic’s products. They are an outstanding company with great products and great support.
- Dell NX1950: I did some research on Dell’s NX1950, but I couldn’t really figure out what it was, to be honest. It looks like a couple of PowerEdge 1950’s (the controllers) with a bunch of disk added to turn it into a SAN/NAS/direct attached device, but in my perusal of VMware forums and other outlets, there was enough concern regarding performance that I didn’t get to the pricing stage with Dell on this product.
- Dell MD3000i: I think this is a good choice for smaller environments that simply need a lot of storage. It’s not expensive, can be installed in a more highly available way and can provide a lot of space. The pricing I received from Dell on the MD3000 was very good. When it came right down to it, though, the EMC AX4 simply provided me with an overall better option from a technical perspective.
- Compellent: Compellent has a very… compelling… solution. It’s okay to laugh. Compellent provides tiered storage capability in an iSCSI SAN. I didn’t get too deep into the details about the product since I couldn’t afford it!
- LeftHand: LeftHand was another early player in the iSCSI market and gains their availability through what they refer to as network RAID. In short, network RAID is a method by which availability it achieved through the use of at least three physical devices. I like LeftHand’s solution because it allows for smaller chunks of growth and, like EqualLogic, as more arrays are added, more network connectivity is added, thus increasing the overall capacity of the system. With LeftHand, it’s easier to add capacity as needed. With EqualLogic, you basically have to double your capacity when you buy a second array, even if you don’t really need that much space. With LeftHand, the upgrade path is a little more smooth.
I’m not going to list the rest of what I looked at as the list would get very long and I’m not sure I could provide much useful information. I will explain my reasoning behind choosing the EMC AX4, though.
I was able to procure my AX4 at an excellent price. My AX4 array is of the iSCSI variety, has dual controllers and 13.8 TB of raw capacity. I actually have two physical units. The DPE (data processing enclosure) holds the dual redundant controllers along with twelve 400 GB 10K RPM SAS disks. The second enclosure, the DAE, holds twelve 750 GB SATA disks and is cabled to the DPE. All told, my per TB cost on the AX4 was around $2,500.
When I’ve previously discussed the AX4 possibility, some of the comments have revolved around the arrays upper limit of 64 hosts, 60 TB of capacity and necessary upgrades for advanced management. As a part of my project, I upgraded to the full Navisphere and Snapshot Manager tool. The price to do so was very, very reasonable and the array’s annual maintenance costs are extremely low. As far as the host limit goes, we have about 20 servers today and I don’t see us growing to the 64 host limit. When it comes to raw capacity, 60TB is a lot of space! If we grow to a point in the next five years where 60 TB isn’t sufficient, we’ll look at another solution, but I simply don’t see it happening. Of course, this 60 TB limit assumes the use of 1 TB SATA disks and we’re using 400 GB SAS, but that’s still a lot of capacity.
Perhaps the biggest drawback of the AX4 when pitted against an EqualLogic or LeftHand array is the fixed controller bandwidth. As physical capacity is added to these other arrays, iSCSI network bandwidth increases. With the AX4, what you buy is what you get. An AX4 solution includes only a single DPE with redundant controllers. Expansion enclosures do not add controllers. However, with the pricing I received, this was an acceptable trade-off for me.
The AX4 is in what I consider the sweet spot for the midsized market. EMC nailed it. The feature set is good, top end capacity is more than sufficient and it fits the budget. EMC touts this array as being a VMware companion and that is our major intended use as well.
Now on to an easy answer: Backup. We’re still using agents on each server to backup to tape. Why? We simply haven’t looked at anything else yet. Our priority was getting storage in place, consolidating our servers and some other projects. We will be looking at different backup methods, including VMware Consolidated Backup, in the near future.
IT Generalist also asked why I prefer an Active/Active controller configuration over an Active/Passive configuration. When I had my EqualLogic PS200e, that unit was configured as Active/Passive and when I asked EqualLogic support about it, they indicated that they run like this in order to provide consistent performance, even when one controller fails. My opinion: In reality, controllers shouldn’t fail a whole lot. In the rare instances that they do, I’m not upset to take a performance hit as long as all my stuff stays up. I’d rather have both controllers running at full bore 99.9% of the time and the array at half capacity only that 0.1% of the time. This may be a simplistic way to look at it, but I think it makes sense.