Hardware Reference
In-Depth Information
FIGURE 4.6: Diagram of file system changes underway at ALCF.
A file is written to disk.
After a period of time, a copy is written to tape|now two copies of the
data exist: one on disk and one on tape (the delay is to avoid writing
files to tape that may be deleted).
After another period of time, if the file has not been accessed it is deleted
from disk (with the only copy being on tape now).
The metadata stays in GPFS and it will appear in a file listing.
If the file is accessed, the system retrieves it from tape automatically.
The delays at each step are configurable and would need to be tuned based
on usage patterns. However, the intent is that the removal from disk would be
a long enough delay (months) that the odds of having to retrieve it are small.
The potential advantages of this system are as follows:
 
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