Re: [9fans] information about filesystems

[erik quanstrom <quanstro@quanstro.net>]

> is there any source where I could read about differences between kfs
> and fossil (also I heard about something like cwfs), about reasons why
> fossil was designed and superceded, when to use which and alike?

steve's summary is excellent.  a few more words about my favorite,
ken's fs

the "worm" partition doesn't really need to be a worm.  it can
be any sort of device.  i currently use aoe targets.  typically coraid
appliances. but i have a few old fses using scsi disks or ata disks
hanging off ide/marvell/ahci controllers.

the big advantage of ken's fs is speed.  at coraid we top out at
>300mb/s file io on a lowly intel 5000 xeon and a old coraid
appliance.  ken's fs is able to serve so quickly because
- it doesn't waste time compressing (compression is slower than
disks these days!)
- it can have a huge memory cache — nearly all of memory.
- it doesn't need to copy between user space and kernel space;
it also doesn't do anything with the mmu except set up 1024
4mb pages on startup.
- it keeps files less fragmented, due to fact that it doesn't
ensure that blocks are globally unique.

ken's fs also tends to be stable enough to be externally
uptime limited.  things like ups batteries and network hiccups
tend to be more disruptive.

here are a few more ken's fs references.
	http://www.quanstro.net/plan9/disklessfs.pdf
	http://www.quanstro.net/plan9/history.pdf

- erik