2011-02-22 10:44 AM
I was told by one of VARs that when having PAM2 cards (we will have 256GB modules) we will have to use dedupe (or we should use it) as PAM2 are A-SIS aware and they run way better when dedupe is enabled (as dedupe tasks will clear a bit PAM2 cache). However I do not have trust in ASIS anymore, and I don't want to use it because of performance issues we experience with dedupe enabled.
But I would like to know how does it combine with PAM2, and if it's really recommended to have dedupe enabled or not (would be nice to have some TR on that topic)
Thanks in advance for your answer.
2011-02-22 11:22 AM
I am not sure whether this qualifies as “have to”, but if you use dedupe, you have less physical blocks to access and they likely are accessed more frequently, which means they have better chances to be cached by PAM.
OTOH, someone (may be, it was you – sorry, do not remember) reported that running A-SIS trashed PAM. If this is really true, and it happens with flexscale.lopri_blocks off, it looks more like a bug – for me A-SIS job definitely qualifies as low priority w.r.t. PAM caching.
2011-02-22 11:34 AM
thx for answer. it was not me about trashing pam, as we just bought new system with pam2. however my design is hard to predict and i can't cause performance issues to our customers even though we would gain extra space. but in our case it takes too much time (1tb vol takes couple hours) and we have lots of volumes so we would definitely overlap dedupe tasks which with snapmirror may cause it even worse...
why do i say about performance impact? because whenever i get a call from customer who says performance is slow, and i check that 2-3 concurrent dedupe tasks are running, when i stop 2 of them, issue seems to be solved.
i environment "dedicated" where maintenance windows are agreed it's just waaaay easier to manage dedupe