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Re: problems with real-time option.

To: linux-xfs@xxxxxxxxxxx
Subject: Re: problems with real-time option.
From: Ramesh K <kram@xxxxxxxxx>
Date: Fri, 13 Feb 2004 12:27:43 +0000 (UTC)
In-reply-to: <20040213002009.GC1158@frodo>
Sender: linux-xfs-bounce@xxxxxxxxxxx
        Thanks Nathan. I wanted to use ramdisk only to store filenames, and the
actual data in realtime subvolume. Thoguht it'll have better performance.
        However I've now repartioned my disk to have two partitions: one of
100GB and the other of 800GB (/dev/sda1 and /dev/sda2 respectively). I'm using
/dev/sda1 as my regular xfs volume (log plus metadata), and configured /dev/sda2
as the realtime subvolume. This is the output of mkfs.xfs:

dop93:~ # mkfs -t xfs -f -d unwritten=0 -r rtdev=/dev/sda2 /dev/sda1
meta-data=/dev/sda1              isize=256    agcount=25, agsize=1048576 blks
         =                       sectsz=512
data     =                       bsize=4096   blocks=25601577, imaxpct=25
         =                       sunit=0      swidth=0 blks, unwritten=0
naming   =version 2              bsize=4096
log      =internal log           bsize=4096   blocks=12500, version=1
         =                       sectsz=512   sunit=0 blks
realtime =/dev/sda2              extsz=65536  blocks=208836967,

dop93:~ # mount -t xfs -o rtdev=/dev/sda2 /dev/sda1 /mnt

        It's been good so far. Now how do I determine the amount of free space
in my realtime subvolume? Do I need to have the realtime subvolume on another
device altogether (instead of another partition) to get better performance?
        I don't know what version of XFS I'm using (it's not v1.3, but the one
packaged with SuSE 8.1). I have new version ( 2.2.1-28) of xfsprogs though.
        In the mean time I also tried to write a 'realtime' file on the realtime
subvolume - but SuSE 8.1 seems to have disabled O_DIRECT and O_LARGEFILE
support. Any clues on that? I'm trying hard to get the realtime subvolumes
working - hopefully it is more deterministic than the regular buffered I/O. Any
info on these lines would be great. Thanks in advance.


> On Thu, Feb 12, 2004 at 03:55:10PM +0000, Ramesh K wrote:
> >
> > Hello,
> >     I'm trying to use realtime subvolumes under Linux (SuSE 8.1, running
> > kernel 2.4.19-64GB-SMP (I know it is very old!!)
> You should be aware that realtime support is marked experimental
> and may not function correctly.  That said, Eric made several
> fixes in this area awhile ago and the last time I tested it, it
> was looking much more stable.
> >     The hardware: I'm using a 3ware RAID controller, and am using RAID level
> > 0 (all eight 120GByte disks together are seen as one disk of 960 GByte 
> > device).
> >     Now I want to use this entire 960 GBytes for my realtime data, and want
> > to place metadata on ramdisk. When I try:
> > dop93:> mkfs -t xfs -f  -d unwritten=0 -r rtdev=/dev/sda1 /dev/ram1,
> >
> >     I get warnings on block size of ramdisk. And when I try to mount the
> What is the warning?
> > device with: mount -t xfs -o rtdev /dev/sda1 - the call never returns.
> >     Am I doing something very gross? Thanks.
> That mount line is incorrect, you need to use something like:
>       mount -t xfs -o rtdev=/dev/sda1 /dev/ram1 /mnt
> It seems odd to be using a ram disk in this way...
> cheers.
> --
> Nathan

Ramesh K
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