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| About this blog: Computers hate me. They really do. Every time I try to do something unusual like add new hardware, something is guaranteed to go wrong. I decided to start writing about my constant problems so that someone else might benefit from my experiences - or at least laugh at them! |
I noticed that my database server was mainly doing reads for (random) index lookups, with the occasional bit of writing. Because of the random nature of access my server was being held back by HD I/O speed; I'd been thinking about moving to a faster drive, a SATA VelociRaptor or perhaps even coughing up for an SAS solution. Cost was an issue, particularly because with my bad luck my storage pretty much has to be redundant (that means at least two drives on RAID1).
After some thought, I came up with a novel idea: mirror the VelociRaptor with a standard drive, and force FreeBSD's gmirror to read only from the VelociRaptor. In effect, this RAID1 array provides a high speed random read with a "standard" speed write. The cost per gig is about $AUD1.50 versus $AUD2.50 if I'd just used two VelicoRaptors. (Now compare this to $AUD0.46 per gig if I'd just used standard drives.....)
A real world example:
ad8 is a 300GB VelociRaptor, ad10 is a standard 320GB drive. Read requests (red) go only to the busy VelociRaptor while the less frequent/frantic write requests (green) are mirrored over both drives.
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Related posts:
Velociraptor HD failed...
VelociRaptor thrashing when the OS is idle
A warning about Western Digital VelociRaptor connector locations
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