Karl,
Why haven't you given the option to upgrade to bigger then 32MB NVRAMs ? It seems as a logical upgrade path for heavy write-based installations.
How can I check what's the utilization of the NVRAM (if my triggers are more "full NVRAM" or "10sec.") ?
Eyal.
Karl Swartz wrote:
This will affect write performance. In essence, there will only be half as much space in NVRAM to hold write data before flushing to disk, so you will most likely end up flushing to disk more often.
Yea, I figured as such, but I was looking for a more quantative answer. Our CPU isn't that taxed, so in theory would we not notice any performance hit? I mean, regardless of the amount of NVRAM, the info has to be written back - I would just imagine that less ram means more writes. How does this factor into the big picture of "performance of the filer" ?
It depends. When a filer boots, it partitions the available NVRAM into two equal chunks. (If it is a member of a cluser, "available" NVRAM is half of the physical NVRAM with the other half belonging to the cluster partner.) Data and metadata writes are logged to the first chunk until one of two events triggers the establishment of a new consistency point on disk, which consists of writing out all of the logged writes while sending new writes to the other NVRAM chunk. The trigger events are
(1) the current chunk becomes full (2) ten seconds have elapsed since the last CP (longer for NetCache)
If your write rate is sufficiently low, such that the timer will trigger the start of a new CP when less than half of the NVRAM chunk is used, then taking out half of the NVRAM should have no performance impact at all. (Someone else mentioned that in an F330, NVRAM will be interleaved if you have 8 MB but not if you have 2 MB -- and may or may not with 4 MB. That's true, and will impact write performance, but if you have relatively few writes and the CPU doesn't have anything better to do, the impact probably won't be significant.)
-- Karl Swartz Network Appliance Engineering Work: kls@netapp.com http://www.netapp.com/ Home: kls@chicago.com http://www.chicago.com/~kls/