R package: hash: save into R objects on disk very slow - r

Question

I am using the great hash package by Christopher Brown. In my use case, I have several thousand keys in the first level, and each related value may save another 1-3 layers of hash objects. When I try to save it using save, it seems to take a really long time.
I then tried save and load on the exact same setup, except a smaller use case with about 100 keys. The save and load work well, except it does seem to take longer than doing the same for usual R objects of similar size.
Is this a known problem, and is there any work around of the speed issue?
My machine setup: Mac OSX 10.6, RStudio 0.98.1091, hash 3.0.1.
The code used to generate the data, and the outcome (in comment) is below:
library(hash)
library(microbenchmark)
create_hash = function(ahash, level1=10, level2=5, level3=2) {
for (i in 1:level1) {
ahash[[paste0('a',i)]] = hash()
for (j in 1:level2) {
ahash[[paste0('a',i)]][[paste0('b',j)]] = hash()
for (k in 1:level3) {
ahash[[paste0('a',i)]][[paste0('b',j)]][[paste0('c',k)]] = hash()
ahash[[paste0('a',i)]][[paste0('b',j)]][[paste0('c',k)]][['key1']] = 'value1'
ahash[[paste0('a',i)]][[paste0('b',j)]][[paste0('c',k)]][['key2']] = 'value2'
}
}
}
}
base1 = hash()
create_hash(base1, 100, 10, 2)
microbenchmark(save(base1, file='base1.Robj'), times=5, unit='s')
# Unit: seconds
# expr min lq mean median uq max neval
# save(base1, file = "base1.Robj") 4.962731 4.987589 5.212594 5.102403 5.316056 5.694193 5
# File size: 1.6 MB
base2 = hash()
create_hash(base2, 1000, 10, 2)
microbenchmark(save(base2, file='base2.Robj'), times=5, unit='s')
# Unit: seconds
# expr min lq mean median uq max neval
# save(base2, file = "base2.Robj") 108.6682 109.2254 110.4126 109.3526 111.1013 113.7154 5
# File size: 16.1 MB