Re: Less disk space with reiser4?

[David Masover <ninja@slaphack.com>]

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Chester R. Hosey wrote:
> Many filesystems claim degraded performance as free space decreases
> beyond a certain threshold. However, they often allow the user to exceed
> this point and accept the decline in performance.
> 
> While Alex's explanation does well to explain why a certain amount of
> free space is required in the case of a commit depending on a certain
> amount of free space, it doesn't quite show that 45 gigs are required to
> cover this requirement on a terabyte of space. Is this a reasonable
> requirement?

Not in my book.  Let me second this.

It's not all that expensive to build a terabyte array.  It's much more
expensive to build a box with 45 gigs of RAM.  People who can afford to
run Reiser4 on a box with 45 gigs of RAM can afford to hire you guys to
patch it.

I propose that the limit should be configurable, and modifiable online
or offline with some sort of tunefs command.  In fact, I propose that
the default should be 5% or the total RAM at time of creation, whichever
is lower.

What if the user upgrades RAM?  Change this value on mount, if the space
is available, and create a mount option to override this behavior.

Performance concerns should be addressed by printing a warning in dmesg,
somewhat like "flushing like mad".  And most filesystems suffer with
more than 75% full, so it's better to educate the users than just steal
a quarter of their space (or even a twentieth).

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