2012-08-01 22:07, opensolarisisdeadlongliveopensolaris пишет:
L2ARC is a read cache. Hence the "R" and "C" in "L2ARC."
"R" is replacement, but what the hell ;)
This means two major things:
#1 Writes don't benefit,
#2 There's no way to load the whole DDT into the cache anyway. So you're
guaranteed to have performance degradation with the dedup.
If the whole DDT does make it into the cache, or onto an SSD
storing an extra copy of all pool metadata, then searching
for a particular entry in DDT would be faster. When you write
(or delete) and need to update the counters in DDT, or even
ultimately remove an unreferenced entry, then you benefit on
writes as well - you don't take as long to find DDT entries
(or determine lack thereof) for the blocks you add or remove.
Or did I get your answer wrong? ;)
zfs-discuss mailing list