The greatest task on any job, has to be product tolerance testing.

We are gearing up for a series of tests that will define what sort of SAN we will be using on the VPS Cloud, the actual tests will be performed early next week, for now we are setting up the hardware for it, once we have done it, we will post the results here in the bog.

Here is the info on what we are planning …

Basically, our data backend will be a SAN consisting of a huge number of virtual disk targets. The way this works is as follows:

  • Each physical storage server (NAS) breaks down its disk array into smaller logical volumes (using LVM), with 1 volume for each virtual machine
  • Each of these volumes is then shared using ATAoE technology across a switched gigabit Ethernet SAN, allowing all the hypervisors to efficiently access any virtual machine’s disks as required

This method allows hypervisors to be fully redundant, allows new storage hosts to be easily added to the SAN, and in the near future will allow full redundancy of storage hosts.


Initially our plan was to use the scenario 1 .. each NAS would consist of 10TB of Raid 5 data, the backups would then reside on separate 10TB (also Raid 5) clusters, if a volume failed, it could be restored into any of the SAN nodes within seconds.

But we then decided we want even greater availability, by RAID-1 the individual NAS themselves, so if a NAS itself fails, a mirror takes over, no need to restore backups (of course, we will still keep the backup nodes, you can never have enough redundancy) .. this will be the case, but not for the January 31st release, as we are still working on the backend code to make this possible.

By keeping the individual nodes at 10TB each, we expected the I/O to be fine, but doubts started to arise lately, and the last thing we want is a 10TB node to become saturated, so a decision was made to do a test, 10TB Raid 5 nodes vs 5TB Raid 10 .. basically, it’s the same config for the nodes, it jut happens Raid 10 halves the available data for the same amount of HD’s than Raid 5 (but you Raid buffs already know that)

Of course, as a tech, I love Raid 10, heck, i’d even use it on the backup nodes if I could .. but the accounting department would be less than impressed `:), no matter how you look at it, Raid 10 doubles the cost of Raid 5, and the more it costs, the more one needs to prove that it’s justifiable …

So come back soon, and we will post our tests results once we have them. 😉