SSD, Overcommit and vSphere5 licensing

vSphere5 licensing has been discussed quite a bit lately, here’s another quick take.

Memory overcommitment has been a VMware staple for many years and has been used extensively in price comparisons especially in the SMB space.

Host Cache (aka local SSD drives) is a new technique for ESXi5 hosts to redirect kernel swap files (for when your overcommited VMs run out of physical memory on the host) onto local, fast SSD drives. See here.

The question is, who will be using these features?

vSphere 5 sets pricing by how much RAM you allocate to running virtual machines (vRAM). For Standard it costs $39/GB for Enterprise $54/GB and Enterprise Plus $44/GB (all prices are from VMware’s online store using 1 year of basic coverage divided by the vRAM entitlement).

A quick check of a couple of new Dell servers puts physical RAM pricing at ~$35/GB
(note I looked at the R715 and R910 with 32,64,128 and 256GB configurations to get an average. Range was $20/GB-$49/GB – both of those figures were R715 at 32 and 256 respectively)

A quick check of Dell server-class SSD (again, the R715 and R910 using 50 and 100GB SATA and 149GB SAS) shows prices at $20/GB for SATA and $30/GB for SSD with a SAS connection.

So per GB:
vRAM entitlement : $39 (STD) / $54 (ENT) / $44 (ENT+)
backed by physical RAM (pRAM): $35
backed by SSD: $20 (SATA) / $30 (SAS)
backed by RAID1 SSD: $40 (SATA) / $60 (SAS)
(if a drive fails my money says any VM with swapped memory will blue screen.)

So, a 4GB VM will cost $156 for licensing plus either $140 to back it fully with pRAM or $160 to back it fully with SSD. Not backing it fully runs the risk of a performance hit if the host needs to swap to the normal storage and unless you start getting tricky with Reservations you won’t know which VM will be swapped.

Overcommit (not backing it fully) can be viable and may increase in popularity, now that the cost of vRAM has doubled (remember vRAM wasn’t a license cost in previous versions, so if you wanted to use 64GB of pRAM you only had to pay for the pRAM itself, not the right to use it.)

Unless you were at the physical limit for RAM in your system and scaling out wasn’t more viable – maybe SSD could be an option, but at twice the price of pRAM does anyone think it will take off?

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One Response to SSD, Overcommit and vSphere5 licensing

  1. Does anyone ever expects to use their .vswp files? No they probably don’t… Still at some point almost everyone gets in to a situation where they are overcommitting because they didn’t take maintenance of multiple hosts into account or maintenance and a failure of a host or just extreme memory pressure. This feature is not a replacement for memory and it will never be. It is a way to prevent to be swapped to slow rotating media… that is something completely different,

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