We don’t normally post about hardware wankery, but this little piece of shininess appeared for free in some of the newer Dell servers we’ve been ordering, and it actually sounds like it’s not an awful hack.
Cachecade is an LSI technology (Dell PERC cards are rebranded gear) that adds a read-cache tier to the RAID logic, in the form of solid-state disks. While SSDs are still too expensive for mass-scale primary storage, they’re cheap enough that you can burn a few hundred bucks and get 50gb worth of faster reads.
The real benefit of this style of read-cache should be for random block reads, where SSDs proverbially drop excrement over rotational media from a great height. The jury is still out for us – we’ve just started using cachecade on a couple of VM hypervisors and a customer DB server, but we’re hoping to see some noticeable impact even on a qualitative basis.
In truth, the performance improvements will be difficult for us to quantify on our own workloads. You can apparently get this functionality if you purchase the new LSI® MegaRAID® CacheCade™ Pro 2.0, but I’d bet that it’s not exposed through something sane (like SNMP) and you’ll be forced to use the perennially-awful MegaCLI tool to get at the data.