Edward Rolison wrote:
I _think_ given the workload I'm putting through one of my set of filers, enabling lopri_blocks is beneficial
When I do, a 'stats show -p flexscale-access' gives me more disk reads replaced, and a better cache hit ratio.
Those two are pretty much the things you should be looking at. I.e. if Disk Read Repl and Cahce Hit Ration goes up, then that's what you want as a setting
However I'm also looking at wafl:wafl:read_io_type and seeing that mostly - my cache module is only servicing about 10% of the IOPs going through my system anyway. Of the remainder, it's a pretty even split between disk/cache.
Add more FlashCache and this will change ;-)
And with 'lopri_blocks' set to on, my cache is churning data faster - but with it off, hit rate drops to <10%.
The faster churning doesn't really matter, if you get more disk reads replaced then AOK. Run with lopri_blocks on.
Primarily looking at:
- total IOPs (there's only one volume on this filer)
- response time.
- Disk utilisation (definitely increases when lopri_blocks is off).
- cache stats as above.
You're good. That's my take on this. There's nothing else you need to look at, of all this is bejhaving the way you indicate here, you're good. It's when it's behaving badly, when it really shouldn't (i.e. protocol latency goes up)that the fun starts...
CP types - mostly this system is doing log_full CPs, and is getting a fairly steady stream of RW IOPs. Most IOs are NFS getattr and lookups though, which are mostly metadata. Of 100K iops, it's about 90% non-RW and 5% read, 5% write.
This is pretty much what my workload is. And don't look for any more metrics than you have described here.
I think I'm right in saying that these metadata IOs are going to be fairly small and thus served out of RAM (mostly) anyway.
Yes. If you don't have enough RAM buy a bigger filer. And add more FlashCache, that's almost always goood (there's a limit of course, when money spent isn't really giving you any more due to too little RAM in the machine.)
I'm also (re) reading TR-3832 - Flash Cache best practice. This is a little more vague than I'd like on figuring out whether 'lopri_blocks' will actually be useful.
I _think_ they are based on a better hit rate, and a better reads-replaced rate. Any read replaced is one that's served from a faster tier, and is therefore 'better' objectively, right?
Yes.
/M