In the QFS manual, there is a section that describe "Mismatched
Striped Groups" where a concatenated volume is composed of multiple
disks/raids.  It describes one usage model of video/audio file case.
However what I don't get - isn't it the same creating 2 different FS
will do the same trick?  What's the difference?  Why does one need to
have that in the same FS?  What's the advantages?

Ernest

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ernestsiu@yahoo.com (Ernest Siu) writes:
> In the QFS manual, there is a section that describe "Mismatched
> Striped Groups" where a concatenated volume is composed of multiple
> disks/raids.  It describes one usage model of video/audio file case.
> However what I don't get - isn't it the same creating 2 different FS
> will do the same trick?  What's the difference?  Why does one need to
> have that in the same FS?  What's the advantages?

You're right, it would be possible to create two file systems for this.
However, allowing two stripe group sizes in the same file system can
simplify administration.

Consider the audio/video case in which a streaming server has separate
audio and video files for each video clip.  If you have two file
systems, these would have to be in separate directories.  If you use
stripe groups, you can place them in the same directory even though
they have differing needs.  This is particularly important when using
an existing application which may be hard-coded to use a particular
directory structure.

Similarly, a data capture application may use a stripe group to allow
image data (for instance) to be recorded very quickly.  The metadata
for each image, however, is probably a small file, and using a whole
stripe group's worth of allocation would be wasteful.  Stripe groups
allow the metadata and image data to reside in the same directory,
even though the image data is allocated with very large blocks and the
metadata is relatively tiny.

In addition, when SAM is included in the picture, using a single file
system allows a single archiver policy to apply to the two classes of
files, allows features such as associative staging to be used between
file classes, etc.

-- Anton

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