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Re: Problems with mkfs.xfs

To: Detlef Vollmann <dv@xxxxxxxxxxx>
Subject: Re: Problems with mkfs.xfs
From: Steve Lord <lord@xxxxxxx>
Date: Thu, 09 Aug 2001 08:37:52 -0500
Cc: Nathan Scott <nathans@xxxxxxx>, XFS list <linux-xfs@xxxxxxxxxxx>
In-reply-to: Message from Detlef Vollmann <dv@xxxxxxxxxxx> of "Thu, 09 Aug 2001 03:55:44 -0000." <3B7209C0.1DDDE1DD@xxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
> Nathan Scott wrote:
> > 
> > hi,
> > 
> > On Thu, Aug 09, 2001 at 02:37:22AM +0000, Detlef Vollmann wrote:
> > > On writing a small testsuite for a simple utility, I hit
> > > several problems with mkfs.xfs (1.2.0):
> > >
> > > Minor problem: syntax
> > > mkfs.xfs does not conform to the mkfs syntax (at least not to
> > > the one described in mkfs(8) on Linux and which I know since
> > > more than 15 years now :-}
> > >   mkfs -t xfs /dev/xxx 1234
> > > produces just an error message on the size parameter :-(
> > >
> > 
> > Hmm... yes, you're right.  If it's a problem, send a patch.
> Probably I should.  Perhaps later.

Take a look at the xfs mkfs source code first, it has many many
calculations based on the size of various things in there to prevent
you from making a non-working filesystem, adding new options is not
as simple as you might think.


> 
> > > Bigger problem: semantics
> > > In the native mkfs.xfs option list, I found nothing that resembles
> > > the size parameter of the original mkfs command.  I had to do
> > > some computations and give size parameters for the different
> > > parts (data and logging).
> > 
> > You're after the -d size=XXXb option, which I think would most
> > closely match the optional [blocks] parameter of mkfs.
> If I read the manpage correctly, that filesystem would not
> fit into a device with size xxxb, as the log is still added.
> 
> > 
> > >
> > > Real problem: size itself
> > > I tried to create an xfs filesystem on a 4MB ramdisk (/dev/ram0),
> > > but I found no combination of option that succeeded.
> > > Did I not try hard enouh or is the lower limit for xfs size
> > > larger than 4MB?
> > >
> > 
> > Yes - the minimum is 16MB, if I remember correctly (ie. the
> > minimum size of one allocation group).
> Ahh, that's serious.  I'll have to find a workaround for that :-{


There is unfortunately no workaround for this, XFS on a floppy would
have been a nice test bed for people, however, there are some minimum
sizes in XFS which prevent this. For deadlock reasons, the log must be
twice the size of the largest potential transaction we can have, this
makes the minimum log size 1200 4K blocks which is already over 4Mbytes.

XFS was designed to scale up, not to scale down ;-)

Steve


> 
> Thanks for the info.
> Detlef
> 
> -- 
> Detlef Vollmann
> vollmann engineering gmbh           Tel: +41-41-4120911
> P.O. Box 5106                       Fax: +41-41-4120912
> CH-6000 Luzern 5 / Switzerland      eMail: dv@xxxxxxxxxxx



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