Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem

Pavel Machek
2009-06-21T06:46:18Z

> > Why is an entire filesystem needed, instead of simply a block driver
> > if the ramdisk driver cannot be used?
> >
>
> >From documentation:
>
> "A relatively straight-forward solution is to write a simple block
> driver for the non-volatile RAM, and mount over it any disk-based
> filesystem such as ext2/ext3, reiserfs, etc.
>
> But the disk-based fs over non-volatile RAM block driver approach has
> some drawbacks:
>
> 1. Disk-based filesystems such as ext2/ext3 were designed for optimum
> performance on spinning disk media, so they implement features such
> as block groups, which attempts to group inode data into a contiguous
> set of data blocks to minimize disk seeking when accessing files. For
> RAM there is no such concern; a file's data blocks can be scattered
> throughout the media with no access speed penalty at all. So block
> groups in a filesystem mounted over RAM just adds unnecessary
> complexity. A better approach is to use a filesystem specifically
> tailored to RAM media which does away with these disk-based features.
> This increases the efficient use of space on the media, i.e. more
> space is dedicated to actual file data storage and less to meta-data
> needed to maintain that file data.

So... what is the performance difference between ext2 and your new
filesystem?

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