Just an FYI.
I installed a hybrid HDD into my notebook (that's an ordinary HDD with several GB's of flash designed to act as a cache). The middle-tier cache concept seems to work reasonably well, it keeps the most-seeked-to sectors in flash for quick(er) access. I can see a clear difference in disk performance whenever my workload changes dramatically. Mostly, it just helps Windows boot faster, and helps MS Office apps load faster.
But the Achilles' heel of any caching design like this is apparent when you do something like, say, boot into another OS. After running Ubuntu for two days, rebooting into Windows felt sloooooow. I guess two days was enough time for full cache replacement, I think this model has 8GByte of flash built in, so that's entirely reasonable. Upon rebooting into Windows, though, launching Outlook and opening a mailbox folder took several *minutes* longer than normal.
It stands to reason that these types of disks would excel in areas where there's strong locality of information... like the NTFS File Descriptor table. And this also explains why performance was utterly awful when using btrfs - locality of metadata is almost zero with that FS.
So, just a hint if you're considering buying this type of disk - consider your workload. If your workload changes often, you'd be better off spending the additional cash on a slightly faster or slightly bigger non-hybrid HDD.
Is anyone using flash as a mid-tier cache in large disk arrays yet? Do they experience the same issue?
-Adam Thompson athompso@athompso.net