VMware VFlash / vSAN

[pcstru]

Is anyone running VMWare stacks using VMware's vFlash or vSAN capabilities? I'm quite keen to use vFlash as a quick and relatively cheap way to deploy a few SSD's and get the benefit of a large read cache to take some of that load away from the SAN. Longer term, I want to replace our main SAN and am wondering if vSAN could be part of that solution. Any feedback on either would be appreciated.

[PotNoodleTech]

Not sure about Vflash, but Vsan is not included in the essentials licence, and is licenced per socket therefore making it prohibitively expensive for most schools who have 2-3 dual CPU physical hosts.

[pcstru]

Thanks. I assumed vSAN would be quite expensive to licence. My experience of SAN's is they cost an arm and a leg too so it's how it compares against that. I think it looks like we would need to tie in replacement of some of the hosts too - which might be difficult to do all at once.

[PotNoodleTech]

Agree. If you've got 2 hosts it won't be too bad, 3 or 4 and you may fall off you're chair.

 

I see no need to get a SAN now that DAS using 12GIG SAS is so good. Just purchased a Dell SAS - 24 disk tray, 48GB SAS connection using MPIO to my 2 x Host servers. MUCH cheaper and faster than a SAN.

[pcstru]

Isn't DAS just local storage, so no vMotion or HA?

[PotNoodleTech]

No it's an external storage tray (in my case with 24 x 2.5" bays) directly connected to both hosts to enable both hosts to use the same storage area thus enabling clustering/ha/etc.

[pcstru]

Ah OK. We have our hosts are spread over two server rooms for resilience. I'm guessing that will not work (veeeery long SAS cables?). I also have gone for dual node SAN's which offer replication and failover in the event of a node failing, which DAS wouldn't offer directly (I'm not sure that vSAN does - it's something to check).

 

Anyone have any recommendations on adding some flash to Dell servers? vFlash offers a read cache (write through) so I was thinking of cheapskating on the eye watering cost of enterprise grade DELL SSD's and sticking a quality PCIE SSD in the hosts for a bit of a cheap(ish) performance upgrade.

[PotNoodleTech]

Either that or a pair of bog standard Intel 3700 SSDs?

 

With that set up it does sound like VSAN may work out cheaper for you as fully duplicating server rooms with SANS etc. is very expensive.

 

With regard to DAS being a single point of failure, yes it is. But as it's pretty much a dumb storage tray with redundant PSU and redundant controller cards and no customised software to go wrong on it, it's already orders of magnitude ahead of a SAN in terms of reliability. Put simply - I don't expect one to catastrophically fail.

Edited July 10, 2015 by PotNoodleTech

[pcstru]

Either that or a pair of bog standard Intel 3700 SSDs?

That would certainly do for the drive but the existing interfaces are SAS so I need some kind of PCIE card to host a SATA drive.

With regard to DAS being a single point of failure, yes it is. But as it's pretty much a dumb storage tray with redundant PSU and redundant controller cards and no customised software to go wrong on it, it's already orders of magnitude ahead of a SAN in terms of reliability. Put simply - I don't expect one to catastrophically fail.

I tend to have "failure expected" as part of the requirement. I'm sometimes disappointed but that disappointment never keeps me awake at night! I am always a little conflicted when it comes to the costs of our SAN. The complexity itself seems to bring an element of unreliability and interesting (more difficult to predict) ways to fail. On the other hand, every time data is written it is written to two arrays in different buildings, which is some comfort unless it's two copies of rubbish!

[PotNoodleTech]

Sandisk do good value SAS SSDs, the Optimus range. Going to try a pair out in my new array.

 

I agree with you. I do think many schools simply over engineer solutions far too much for the level of risk presented. This is often compounded by companies that want to sell you the latest greatest thing. "Primary school? I think you need EMC storage mate"

 

The main Areas of risk are 1) Disk, 2) x FAN, 3) x Power supply. Almost everything else tends to be damned reliable (as in can run 5-8 years non stop without a fail).

 

If you are redundant on the disk, psu, fans with hot swap and couple that with a 5 year on site same/next day warranty you've mitigated 95+% of the risk IMHO. Mitigating the remaining 1-5% of risk comes at great cost.

 

I also agree that the massive amount of complexity of a SAN and the reliance on one particular company to support their customised software/hardware is a big issue and actually reduces reliability and increases risk to some extend.

 

No one size fits all solution!

[pcstru]

Sandisk do good value SAS SSDs, the Optimus range. Going to try a pair out in my new array.

Looking at those exposes another annoyance. Amazon US vs Amazon UK. Grrrrrr.

 

Care to say who are you using for supply?

[pcstru]

Just for anyone who might be interested. vFlash seems to require Enterprise Plus licensing, which for our dual processor Enterprise licensed hosts would be ~£700 to upgrade the licence and an increase every year for basic support of £50 per year (I seem to be being quoted a one off cost of £325 per host to upgrade support for the remainder of this year which doesn't seem to make much sense, so the £50pa might turn our to be substantially more). Then there is the cost of suitable SSD. For this I'd look at a PCIe based device, something like the Kingston 480GB HyperX Predator PCIe SSD with Adaptor. So the cheapest for us per host looks to be around £1500.

 

For that VMWare suggests I should be able to double the read performance at the application level of a fairly typical database application where the read IO is 90% or more of the write load. I'd also expect that to have benefits even for guests running on hosts which are not making use of vFlash because the Read load on the SAN should be reduced.

 

Worth it? Only you can decide!