Subject: Re: SPARSE files considered harmful - please revert
From: "Bill C. Riemers" <[email-masked]>
To: "Max Bowsher" <[email-masked]>
Cc: <[email-masked]>
Date: Mon, 19 May 2003 12:46:19 -0400

> Um? By my understanding, making a file sparse can never be dangerous. It
can
> cause sub-optimal performance, but code reading the file doesn't have to
be
> aware of anything special - the OS takes care of it.

I remember there use to be a warning the man page that file system holes can
cause seek offsets to be wrong for programs that do seek's across or into
hole boundries.  The original Linux code only handled when code was loaded
as a result of an mmap which happens for exec's and dlopen.  It could be by
now these restrictions have been eliminated.  I notice the latest GNU cp
info page lists sparse files a filesystem capacity not a kernel capability,
and the logic for --sparse=auto simply copies a file as-is, nothing smart
like checking for the execution bit.

I looked through the NTFS document on MSDN.  It seems at least for NTFS
there is no restriction on what types of files can be sparse.  Of course, if
you make files sparse that are going to be accessed with RW operations, you
are going to fragment the file.

                                            Bill

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