My datacenter says that each rack has primary and backup power on each rack. I assume this means there is a UPS for each server. Therefore, do I have any need of getting a BBU for the following setup?
Intel Cherry 520 SSD x 4 RAID 10
LSI-9260 with WRITEBACK CACHE ENABLED
I have heard that without a BBU the data in the cache could be lost. Since my needs aren't mission-critical, I can afford to lose some data. But would the rest of the data on the HD be corrupted?
Best Answer
File systems write more than just data to HDDs; they also write metadata. The danger of data loss isn't so much that your most recent results file goes missing as that the metadata becomes corrupt, making the file system inconsistent and unmountable. Corrupt filesystems can lose much more data when they're fscked.
Normally one would choose a journalling filesystem to minimise the danger of this, but with write-cached RAID hardware this may not help, as the hardware has essentially lied to the OS about what has actually been written to disc (considering a write to the cache to be sufficient). Power loss means you may still end up with an inconsistent, and thus later a roached, file system.
No RAID array I know of considers unbacked write-cache to be a good idea, and most of them disable writeback cacheing if the cache battery goes flat. They may have a point.