FATA disk performance for VMware

Question

We are moving to the dataceneter and planning to have tiered storage on EVA4400 - FC RAID 10 for SQL databases and RAID5 across 24 FATA 1TB disks form VMware ESX guests.HP is describing FATA disks as suitable for near online storage, however I am not convinced that 24 spindles will not be enough for running VMWare for 3 ESX servers.
Does anyone has opinion on why this could be a such a bad idea?

Answer 1

I'm a big EVA customer and fan, and I have a lot of those exact 1TB FATA disks and think they're great BUT there's something you need to know. The first box we had with those in saw an enormous number if drive 'failures' within it's first year, some were real requiring new disks, many just eject/reseats - the root cause of the problems were that we run out data centers at a steady 19C and we were told that this was too cold and also that the disk, being a mid/near-line model was specifically not capable of a >30% duty cycle and we'd been using them 24/7. The 450/600GB 15krpm disks are perfect but these 1TB ones were the bain of our lives until we started treating them as they were meant to be treated. Hope thus helps somehow.

Answer 2

Honestly, the root partition of modern OSs has very low IOP requirements. Most libraries and executables are cached in RAM and the needs of services like logging, etc are very light.

The only way to tell for sure though is to calculate the IOP requirements of your guests and see if the disk can handle it. But from my gut feeling 24 spindles even seems overkill for 3 guests.

Answer 3

24x1TB in a single RAID5 set strikes me as very risky due to rebuild times and the high probability of another disk failing during that rebuild (and you losing your entire set).

RAID6 is a much, much safer alternative in this case, although you will lose a bit of write performance. All the more reason to measure your I/O as well as I/O patterns. You need read IOPS, write IOPS, and the percentage of sequential to random I/O.

As for where to get this data, I assume you are not buying direct - leverage your reseller to get you a copy of HP's sizing tools (they MUST have something for pre-sales use) which will gather this data for you and aggregate it into some actionable recommendations.

Answer 4

They are covering their bases I would imagine. They want you to buy FC for a couple reasons...one is price...they want to sell a costlier product of course.

However, they also know that if you can afford it and you buy it, FC disk has the least chance of dissatisfaction from a customer based on performance issues. This is especially true of virtualized environments where iops are in effect consolidated (i.e., disk i/o for how many dozens or hundreds of servers running against relatively few disks). The "bad idea" part comes in when there's a customer that spent good money but didn't get the performance they needed either for whatever reason.

As you're guessing, 24 spindles of non-FC disk may well be more than fine for your workloads. For regular/moderate workloads of heterogeneous iops, it wouldn't surprise me to find that this would be adequate for 3 ESX hosts' worth of guests (especially if we're not talking really high numbers of guests per host).

As joshperry says, it's really a matter of working out your iops...once you know that, you can make an informed choice about whether or not the value-proposition of the FATA spindles works for you.