Re: Speed Disk vs Defrag

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John John (MVP) wrote:
Bill in Co. wrote:

The cluster points to the next cluster for files that span clusters,
the
FAT only points to the first cluster that a file uses, the clusters
point to the next cluster.

That is how it works with FAT/FAT32, but it doesn't work like that at
all
with NTFS. On NTFS that information is all kept as attributes in the
MFT, the file system does not need to flip trough each individual
cluster to find the next one, it's all held in a Virtual Cluster Number
to Logical Cluster map (VCN-to-LCN) in the file's data attribute.

That sounds like a more sensible and robust approach, since you don't
have
to go out and read all the disk clusters to find out where the next one
is
(and pray that one of them isn't corrupt, breaking the chain).

That is not really how it works, (on FAT) the clusters are daisy-chained
in the FAT, the operating system doesn't open successive clusters to
find out where the next one is, it reads that information in the FAT.
The first cluster information for the file is found in the Directory
entry and the other cluster information along with the last cluster is
read from the FAT. In any case, if a cluster in the chain is corrupt
the whole file is usually unreadable or corrupt anyway, chkdsk can
locate and try to repair these bad clusters but most of the time the
recovered clusters are of much use and the corrupt files are not easily,
if at all repairable.

John

OK (and I probably should have known this).
But above, I thought you had said that "the file system (in XP) does not
need to flip through each individual cluster to find the next one", and I
mistakenly thought you were implying that FAT was that way (in contrast with
NT). But maybe you're talking about going through the entries within the
table itself (FAT or MFT).


.

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