On Fri, 18 Feb 2000, Bruce Sterling Woodcock wrote:
Basically, it will effect your write performance. Less NVRAM means it can cache fewer writes, thus having to write to disk more often.
This is not necessarily true. It will affect the speed of some bursty writes where there might not be enough space in the NVRAM to log the complete write stream. If the writes are continuous no loss of performance should be noticed, i.e. the bottleneck will be the speed of writing to disk. In fact, since the number of transactions in the NVRAM will be smaller the banks will clear faster allowing more data to be logged quicker. As I understand from NetApp documentation, and please correct me if I'm wrong, at no point is the NVRAM used as a cache during normal operation. It serves only as a log that is written to, but not read unless a reboot occurs. Although the amount of NVRAM does affect the performance of the write cache, especially during frequent rewrites of the same block, I'm not sure how many applications/NFS stacks actually put out such a mix of ops.
It could also mean that disk allocation will be a little less efficient and possibly increase the chance of disk failure over the long run.
Perhaps. This would be especially true in the abovementioned scenario of continually rewriting the same block.
If you don't really notice the difference on your filer, chances are it is not often very heavily loaded and doesn't experience a lot of heavy write traffic.
Or it is heavily loaded all the time, but the same blocks aren't very frequently overwritten, i.e. the write cache serves very little.
Tom