[R] ff package: ff objects don't reload completely on NFS drives from a different machine

[Hao Cen]

Hi ff users and Jens,

I am using the ff package and it has been working great. Recently I
noticed an unexpected behavior in the ff package --  when I save an ff
matrix on one machine to an NFS drive and load it on another machine from
the save NFS drive,  I got quote a lot of zeros in the matrix. The
following code reproduces the error

mat = matrix(1:25, 5)
matFF = ff(mat, dim=dim(mat),  dimnames = dimnames(mat),
		dimorder = c(2,1),
		filename=  "~/m.ff", overwrite=TRUE)
save(matFF, file = "~/mat.ff.rda")
load(file = "~/mat.ff.rda")
open(matFF)
matFF

If I execute all the six lines at one machine. Everything works fine.
However, when I only execute the last three line at another machine, I got

> matFF
ff (open) integer length=25 (25) dim=c(5,5) dimorder=c(2,1)
     [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    0
[2,]    0    0    0    0    0
[3,]    0    0    0    0    0
[4,]    0    0    0    0    0
[5,]    0    0    0    0    0

If the matrix is larger, say mat = matrix(1:20000, 5), I would get the
following -- dozens of zeros at the end.
 ff (open) integer length=20000 (20000) dim=c(5,4000) dimorder=c(2,1)
      [,1]  [,2]  [,3]  [,4]  [,5]  [,6]  [,7]  [,8]   [,3993] [,3994]
[,3995] [,3996] [,3997] [,3998] [,3999] [,4000]
[1,]     1     6    11    16    21    26    31    36 :   19961   19966  
19971   19976   19981   19986   19991   19996
[2,]     2     7    12    17    22    27    32    37 :   19962   19967  
19972   19977   19982   19987   19992   19997
[3,]     3     8    13    18    23    28    33    38 :   19963   19968  
19973   19978   19983   19988   19993   19998
[4,]     4     9    14    19    24    29    34    39 :   19964   19969  
19974   19979   19984   19989   19994   19999
[5,]     5    10    15    20    25    30    35    40 :       0       0    
  0       0       0       0       0       0

I tried set caching =  "mmeachflush" in the ff function but it doesn't
help.  My computing enrionment is linux 64 bit, R 2.10, ff 2.1.

If you know what causes the issue or how to solve it, please let me know.
I highly appreciate.

Jeff