A question that I get all the time when talking to people about storage is something along the lines of "How can I get performance numbers from my {Insert Company Name Here} sales guy?"
The short answer to that question is that you can't. No storage vender that I've ever run across will give you hard numbers on what their array can handle. The answer for that is very simple; it totally and completely depends on the workload that you are going to throw at the array. It also depends on the cache size that you install, if you've got any sort of flash cache installed and configured (PAM cards in a NetApp, EFDs in an EMC array) and how much flash cache you've got if you do have it.
If the venders give you numbers and you aren't able to hit those numbers because your workload is different from their test workload then you've now got a case to yell, scream and possibly file a law suit against them for false advertising. Don't ever take the numbers that you see on the marketing material at face value. These numbers are best case with very specific workloads which are probably nothing like what you are going to see in the real world.
Remember that storage arrays (and any storage that isn't flash based) has spinning media within it. The performance that you can get from those disks will really depend on several things including:
- The workload that you put the disks under
- How random the IO is
- What else is using the spindles
- How much cache you have installed
- How the cache is configured for reads vs. writes
- If the back end ports are maxed out
- If the front end ports are maxed out
- If the fiber channel or Ethernet (iSCSI) switches are maxed out
- Block size
- How the array is tuned
Fortunately all is not lost, what you can do is ask to talk to some existing customers that will have a similar sized unit to what you are looking to purchase. Odds are your sales person will have some customers lined up already that he can give you on the spot, not all do so the sales person may need to make a few phone calls so give them a day or two if needed.
These customers will usually be pretty candid with you (an NDA may be needed) about their setup and workloads and what sort of performance they are seeing in the real world.
Hopefully this helps you get the information that you need to get the performance that you are looking for from your storage array vendors.
Denny
