chunk management on couchbase

I'm search information about chunk management on memcaches-type buckets and couchbase-type bucket (I'm coming from memcached and have custom -f parameter).
¿how couchbase manage chunks? ¿If I fill the cache with 100k chunks, and then I need to store another value with another lenght, couchbase act like memcached (in certain cases, cannot do it) or have another behavior?
¿Are this behavior the same for memecached bucket and for couchbase bucket?
I'm asking about this because our application sometimes fill memcache with chunks of one type size, and I need to restart memcached server to clean slabs distribution (I see a lot of free memory but start to get evictions, our timeout average is about two hours).
I know the lasts releases of memcache have a slab relocator ¿do you implement something like this on your custom version of memcache?
I'm evaluating the posibility to use couchbase to replace our memcached server.
Thanks in Advance.

Fercho.