xfs + lvm on software raid5

[Alexander Bergolth <leo@xxxxxxxxxxxxxxxxxxxx>]

Hi!

I'd like to create a xfs-formatted filesystem in an lvm logical volume 
that resides on a software raid5 device.

Searching the list archives, I've found that performance should be ok 
using an internal log for kernel versions > 2.4.18. Additionally, I 
found a recommendation to use log version 2.

However, when creating the filesystem, the kernel reports that the cache 
buffer size is reduced to 512 bytes:

# mkfs.xfs -l version=2 /dev/vg_raid5/lv_images
raid5: switching cache buffer size, 1024 --> 512

Are there additional arguments needed for mkfs.xfs?

The first reduction of cache buffer size occurs when activating lvm:

LVM version 1.0.7(28/03/2003) module loaded
loop: loaded (max 8 devices)
raid5: switching cache buffer size, 4096 --> 1024

Does this mean a performance penalty? Is there a way to avoid these 
switches?

Is it still recommended to use an external log? How should the log be 
configured?

Thanks in advance,
--leo

P.S.: Additional info:

# cat /etc/fedora-release
Fedora Core release 1 (Yarrow)

# uname -r
2.4.22-1.2115.nptl_22.rhfc1.at

# rpm -q xfsprogs
xfsprogs-2.6.2-0_7.rhfc1.at

# cat /proc/mdstat
Personalities : [raid5]
read_ahead 1024 sectors
md0 : active raid5 hdg1[0] hdi1[1] hdk1[2] hdm1[3] hdo1[4]
      976751616 blocks level 5, 32k chunk, algorithm 2 [5/5] [UUUUU]

# mkfs.xfs -l version=2 /dev/vg_raid5/lv_images
meta-data=/dev/vg_raid5/lv_images isize=256    agcount=16, 
agsize=8192000 blks
         =                       sectsz=512
data     =                       bsize=4096   blocks=131072000, imaxpct=25
         =                       sunit=0      swidth=0 blks, unwritten=1
naming   =version 2              bsize=4096
log      =internal log           bsize=4096   blocks=32768, version=2
         =                       sectsz=512   sunit=0 blks
realtime =none                   extsz=65536  blocks=0, rtextents=0

# pvdisplay /dev/md0
--- Physical volume ---
PV Name               /dev/md0
VG Name               vg_raid5
PV Size               931.50 GB [1953503232 secs] / NOT usable 64.19 MB 
[LVM: 186 KB]
PV#                   1
PV Status             available
Allocatable           yes
Cur LV                1
PE Size (KByte)       65536
Total PE              14903
Free PE               6903
Allocated PE          8000
PV UUID               d63Tg4-A41Z-4JXb-FwuV-wIik-QuVh-k2XW7E

# vgdisplay /dev/vg_raid5
--- Volume group ---
VG Name               vg_raid5
VG Access             read/write
VG Status             available/resizable
VG #                  0
MAX LV                256
Cur LV                1
Open LV               0
MAX LV Size           2 TB
Max PV                256
Cur PV                1
Act PV                1
VG Size               931.44 GB
PE Size               64 MB
Total PE              14903
Alloc PE / Size       8000 / 500 GB
Free  PE / Size       6903 / 431.44 GB
VG UUID               1f13FE-qPVM-1CSB-0gAu-Fe07-5TlS-ElliwA

--
-----------------------------------------------------------------------
Alexander (Leo) Bergolth                          leo@xxxxxxxxxxxxxxxxx
WU-Wien - Zentrum fuer Informatikdienste       http://leo.wu-wien.ac.at
                 Computers are like air conditioners -
           they stop working properly when you open Windows