A rolling upgrade from 0.98.x to 1.0.x works (TODO: Verify!!!!). The two versions are not binary compatible.
In here we list important changes that are in 1.0.0 since 0.98.x., changes you should be aware that will go into effect once you upgrade.
You may have made use of this configuration if you are using BucketCache.
If NOT using BucketCache, this change does not effect you.
Its removal means that your L1 LruBlockCache is now sized
using hfile.block.cache.size -- i.e. the way you
would size the onheap L1 LruBlockCache if you were NOT doing
BucketCache -- and the BucketCache size is not whatever the
setting for hbase.bucketcache.size is. You may need to adjust
configs to get the LruBlockCache and BucketCache sizes set to
what they were in 0.98.x and previous. If you did not set this
config., its default value was 0.9. If you do nothing, your
BucketCache will increase in size by 10%. Your L1 LruBlockCache will
become hfile.block.cache.size times your java
heap size (hfile.block.cache.size is a float between 0.0 and 1.0).
To read more, see
HBASE-11520 Simplify offheap cache config by removing the confusing "hbase.bucketcache.percentage.in.combinedcache".