This will be a quicky, but I felt it deserved it's own post. I get a lot of questions regarding the purpose of NVRAM, it's a bit of an enigma, so I thought I'd clarify it functionality.
Here's what it is NOT:
1. Performance Acceleration Card
2. Read Cache
3. Write Cache
3. Used to calculate parity
4. Used by WAFL to map where data should be placed on disk
NVRAM's is a short term transaction log and it enables RAM to coalesce writes to minimize head spin and writes to disk. While those writes are in RAM, they are mirrored to NVRAM. All of the goodness and logic built into ONTAP and WAFL are made possible due to the insurance NVRAM gives to it. If the power goes out, all of those writes in RAM are gone, so NVRAM steps in and flushes all of it's contents to disk since it has a battery backup. This way nothing is lost! So NVRAM doesn't make writes more efficient (that's somebody else's job), it's there to catch data if there's a power outage.
Until Next Time!
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