My understanding is that "evicted" means valid blocks removed from PAM (i.e. to free space) while "invalidated" means blocks that were changed (i.e. by client write) so copy is no more actual.
--- With best regards
Andrey Borzenkov Senior system engineer Service operations
-----Original Message----- From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Robert McDermott Sent: Monday, September 19, 2011 11:46 PM To: toasters@teaparty.net Subject: Flash Cache statistics question: Invalidate vs Evict?
I'm trying to analyze the performance of a Flash Cache (PAMII) module and can't seem to find a detailed definition of the "inval" and "evict" metrics. All the documentation simply states the obvious with the very unhelpful "blocks evicted/invalidated from cache per second". Both eviction and invalidation are removal of blocks from the cache, but what I want to know is why are they removed. Essentially what causes an eviction verses an invalidation? Is a block "evicted" because it was never used and a timer expired? Is a block "invalidated" when the cache is full and a useful block is thrown out to make room for a new block?
Thanks,
-Robert
stats show -p flexscale-access
Cache Reads Writes Disk Reads Usage Hit Meta Miss Hit Evict Inval Insert Chain Blocks Chain Blocks Replaced % /s /s /s % /s /s /s /s /s /s /s /s 0 0 0 0 0 0 0 0 0 0 0 0 0
Here are the definitions for those counters: Cache Usage: How much data is currently stored in the module(s) Hit: The 4kB disk block cache hit per second Meta: The 4kB metadata disk block cache hit per second Miss: The 4kB disk block cache missed per second Hit %: The percentage of total hit/miss Evict: The 4kB disk blocks evicted from the cache per second Inval: The 4kB disk blocks invalidated from the cache per second Insert: The 4kB disk blocks inserted into the cache per second Reads Chain: The number of read I/O chains per second Reads Blocks: The number of 4kB disk blocks read per second Writes Chain: The number of write I/O chains per second Writes Blocks: The number of 4kB disk blocks written per second Disk Reads Replaced: The number of reads that would have gone to disk that were replaced by the cache per second _______________________________________________ Toasters mailing list Toasters@teaparty.net http://www.teaparty.net/mailman/listinfo/toasters