RPS IV from OVH (Ireland)

Title: RPS IV
Provider: OVH (Ireland)

Transfer: Unlimited Currency: €

Setup: 0.00 (ex VAT) Monthly Cost: 29.99 (ex VAT) [In Euros: €Formatting error In US Dollars: $Formatting error]

Detailed Notes:

Disclaimer: We make use of OVH servers ourselves

This is one horse of a dedicated server (actually a Real Private Server) with "too good to be true" specifications for the price. This Phenom II processor is nearly equal to a Intel Core2 Quad Q6600 and it has oodles of fast RAM, memory bandwidth, 1.5Mb of fast L2 cache and 6Mb of shared L3 cache. This is a dream low end dedicated server no doubt, and it should handle even gruelling server loads with ease.

You are surely thinking by now "there must be catch" and indeed there is: its storage is a SAN which means that it is a cluster of fast hard drives sitting on a network connection. The benefit of SAN storage is VPS-like ease of instance migration and low management overheads, so one  fuses all the benefits of a VPS with all the benefits of dedicated hardware. Surely this is all good no?

Sadly no - we think that the RPS is a little too ahead of its time. While the SAN can push data at up to NIC speed (100Mbit) at up to maybe 8Mb/sec which is okay, this isn't actually the problem: it's the latency of operations on that SAN which according to our own testing sits at around 90ms. Because most software running on Linux isn't really written to make use of async i/o, five sequential disc accesses - hardly uncommon in a single operation - turns into a half second pause - which means your server regularly hangs for half a second which is unacceptable. This effectively makes the OVH RPS idea - while very novel and having a lot of potential - fairly useless for most dedicated server use cases which is an almighty shame.

The OVH RPS does however have a bog standard USB flash drive plugged in which is usually used as the swap device - this device will read at about 8Mb/sec and with latency of about 1.2ms, but writes are extremely slow as is normal on a bog standard USB drive. One can fiddle with the system to make it boot from the USB key which certainly improves the usability, but ultimately one can only make so much of a silk purse from a sow's ear. I would just love if they could plug in a low capacity 1" USB microdrive - that would make the RPS far more interesting.

The OVH RPS is undoubtedly ahead of its time - Linux will soon be gaining the ability to make far better use of flash memory as a non-volatile disc cache and so that the latency of that SAN could be somewhat ameliorated e.g. if we had BTRFS stable we could do much. However it really needs a 10Gbit dedicated SAN network port on there (and a 100Mbit, or even 10Mbit "internet" port) for it to make any sense - too many people try seeding torrents from the OVH RPS for which a SAN is really, really not suitable (i.e. randomised high bandwidth i/o which no predictive strategy can cache). When sharing one 100Mbit network port one cannot avoid unreliable behaviour. I also wish they'd migrate RPS users on the basis of disc i/o, so those who hammer the SAN all get stuck on the same SAN while anyone who barely touches it gets a totally separate SAN - this would immensely improve the RPS experience.

Pros:

Outstanding dedicated hardware specs at an amazing price. A novel and high potential solution. If you're willing to copy the system into tmpfs and run from there then you have an amazingly fast system.

Cons:

Unusable due to very high and unpredictable storage access latency. It's definitely ahead of its time, but that time will come soon as software support catches up.

Verdict:

Wonderful idea and maybe an option for a very restricted set of use cases, but until the latency issue is fixed you should consider almost any other option.