bad performances on compressed ext2 on CD-Rom

David Monniaux (David.Monniaux@ens.fr)
Wed, 17 Nov 1999 15:33:04 +0100 (MET)


Hi all,

the Demolinux project (http://www.demolinux.org) is designing CDs that can
boot and run Linux all from a CD-Rom. As the capacity of a CD is quite
limited, it was thought a good idea to use ext2 on-the-fly compression.

Two methods have been tried:
- a big file on an ISO-9660 filesystem stored on the CD-Rom, containing an
ext2fs+compression partition;
- two partitions on the CD-Rom, the second of which is ext2fs+compression.

Both methods do work, but extremely slowly (6 minutes to load Netscape,
for instance).

The problem is tricky, since doing the same but with the ext2 partition in
a file on an ext2fs hard drive partition yields fast access times.

We suspect some bad interaction between e2compr and the CD-Rom layer;
perhaps e2compr accesses the filesystem in patterns the CD-Rom driver is
not optimized for.

Has anybody got ideas on this?

Regards,

---
David Monniaux     Tel: +33 1 44 32 20 66    Fax: +33 1 44 32 20 80 
Laboratoire d'informatique de l'École Normale Supérieure,
45 rue d'Ulm - 75230 PARIS cedex 5 - FRANCE

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