Date: Mon, 17 Dec 2001 01:34:27 +0000 From: Tony <tony@ubik.demon.co.uk> To: Greg Lehey <grog@FreeBSD.org> Cc: freebsd-hackers@freebsd.org, Terry Lambert <tlambert2@mindspring.com>, Hiten Pandya <hitmaster2k@yahoo.com> Subject: Re: [SUGGESTION] - JFS for FreeBSD Message-ID: <JGny5rAjuUH8IwoW@ubik.demon.co.uk> In-Reply-To: <20011211182856.A67986@monorchid.lemis.com> References: <20011210220153.50612.qmail@web21102.mail.yahoo.com> <3C15AB82.FDF598A8@mindspring.com> <20011211182856.A67986@monorchid.lemis.com>
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In article <20011211182856.A67986@monorchid.lemis.com>, Greg Lehey
<grog@FreeBSD.org> writes
>On Monday, 10 December 2001 at 22:45:22 -0800, Terry Lambert wrote:
>>
>> No, it's not. The Linux JFS is derived from the OS/2 JFS code, not
>> the good AIX JFS code.
>
>That's correct, but note that AIX is moving to this code base too, so
>it's not as if it's second-rate. From what I've seen of the
>structures, JFS2 is *much* better than JFS1. I haven't compared
>performance.
I have had a little look at the online documentation for IBM's Linux JFS
project, from Steve Best & Dave Kleikamp.
A few things caught my eye that would dissuade me from using Linux JFS
as a base for FreeBSD:
1. "JFS only operates on meta-data ... It does not log file data or
recover this data to a consistent state." [JFS overview]
"The logging style introduces a synchronous write to the log disk
into each inode or vfs operation that modifies meta-data." [JFS
overview]
This doesn't sound any more robust than FreeBSD's current
Softupdates. JFS wins though as fsck is faster on a reboot ...
Does AIX JFS log any file data?
2. "The minimum file system size supported by JFS is 16Mbytes." [JFS
overview]
"JFS will not support diskettes as an underlying file system." [JFS
overview]
I believe AIX JFS does support diskettes / removable media.
3. Linux JFS does not support AIX JFS volumes. [various places]
I am not clear whether this is inherent in some data structures
being different, or just that Linux doesn't process LVM info.
JFS on AIX is "backward compatible" with Enhanced JFS (JFS2).
4. The Linux JFS driver is noticeably incomplete [from JFS todo list]:
o SMP bugs.
o Only 4096 byte block sizes currently supported.
(512, 1024 and 2048 should be available too.)
o No defrag tool.
o FS resizing is not yet available.
o Log file must be on the JFS partition.
o Disk quotas are not currently supported.
o Extended Attributes and Access Control Lists are not functional.
5. "JFS is still guru-friendly (meaning that you need a Linux guru on
hand), but it will eventually grow into administrator-friendly."
[JFS FAQ]
I'm not sure what this means, possibly just that the FS utilities
and man pages need some work.
Although the "I .. never found un-resolvable problems" in the same
paragraph is a shade short of a ringing endorsement of
reliability. (Linux JFS was announced in May 2000, so there has
been some time to work on this.)
Undoubtedly JFS on FreeBSD would be expected to work with Linux JFS
volumes, but inter-operation with AIX JFS & JFS2 is also desirable.
My questions at this point are:
* is there any IBM material, white papers or whatever, that I could
study to find out about JFS(2) on AIX?
* where is a good place to start learning about FreeBSD file systems,
specifically UFS?
Tony
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