Just reading through the wiki on this and a few things are unclear, so
I'm hoping someone can clarify.
1) readahead
- Is there any point in using this on systems where the interconnect <=
1Gb/s? The wiki implies there is no point in this, but doesn't quite
state it explicitly.
- Is there any point in using this on a server that is also it's own
client when use with replicate/afr? I'm guessing there isn't since the
local fs will be doing it's own read-ahead but I'd like some
confirmation on that.
2) io-threads
Is this (usefully) applicable on the client side?
3) io-cache
The wiki page has the same paragraph pasted for both io-threads and
io-cache. Are they the same thing, or is this a documentation bug? What
does io-cache do?
Finally - which translators are deemed stable (no know issues - memory
leaks/bloat, crashes, corruption, etc.)?
Any particular suggestions on which performance translator combination
would be good to apply for a shared root AFR over a WAN? I already have
read-subvolume set to the local mirror, but any improvement is welcome
when latencies soar to 100ms and b/w gets hammered down to 1-2.5 Mb/s.
Another thing - when a node works standalone in AFR, performance is
pretty good, but as soon as a peer node joins, even though the original
node is the primary, performance degrades on the primary node quite
significantly, even though the interconnect is direct gigabit, which
shouldn't be adding any particular latency (< 0.1ms) or overheads,
especially on the primary node. Is there any particular reason for this
degradation? It's OK in normal usage, but some operations (e.g. building
an big bootstrapping initrd (50MB compressed, including all the gernel
drivers) takes nearly 10x longer when the peers join than when the node
is standalone. I expected some degradation, but only on the order of
added network latency, and this is way, way more. I tried with and
without direct-io=off, and that didn't make a great amount of
difference. Which performance translators are likely to help with this
use case?
Gordan
