Performance of packet writing: Blocksize matters

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Hi list,

I have massive performance problems when using the standard approach via an=
=20
udf file system. The disk spins up and down all the time, reducing my write=
=20
speed to about 800k/s. My disk cache is maxed out and 'sync'ing takes ages.=
 I=20
see this with and without the pktcdvd driver with DVD+RW and DVD-RAM media.

The classical mkisofs route works as expected. Feeding the packet driver wi=
th=20
4k blocks (mbuffer -s 4096) results in the full advertised 8x DVD writing=20
speed:

tar -cvM -L4500000 -f - /mnt/data/backup/debian-2005-02-06.tar.gz /mnt/data=
/backup/snapshots/daily.0/ |
mbuffer -m 1000k -s4096  -P 10 > /dev/pktcdvd/dvdrw

Without the -s 4096 option I get the same low performance behavior. I also=
=20
tried different buffer sizes in the kernel module and the experimental writ=
e=20
caching.

What's wrong and how can I help improving the packet driver?

Thank you very much!

Johannes Nie=DF

stingray ~ # dvd+rw-mediainfo /dev/hdc
INQUIRY:                [HL-DT-ST][DVDRAM GSA-4163B][A106]
GET [CURRENT] CONFIGURATION:
 Mounted Media:         1Ah, DVD+RW
 Current Write Speed:   8.0x1385=3D11080KB/s
 Write Speed #0:        8.0x1385=3D11080KB/s
 Write Speed #1:        6.0x1385=3D8310KB/s
GET [CURRENT] PERFORMANCE:
 Write Performance:     6.0x1385=3D8310KB/s@[0 -> 112639]
                        8.0x1385=3D11080KB/s@[112640 -> 2295103]
 Speed Descriptor#0:    02/2295103 [email protected]=3D4584KB/s [email protected]=3D11080=
KB/s
 Speed Descriptor#1:    02/2295103 [email protected]=3D4584KB/s [email protected]=3D8310K=
B/s
READ DVD STRUCTURE[#0h]:
 Media Book Type:       00h, DVD-ROM book [revision 0]
 Media ID:              RICOHJPN/W21
 Legacy lead-out at:    2295104*2KB=3D4700372992
READ DISC INFORMATION:
 Disc status:           complete
 Number of Sessions:    1
 State of Last Session: complete
 Number of Tracks:      1
 BG Format Status:      suspended
READ FORMAT CAPACITIES:
 formatted:             2295104*2048=3D4700372992
 26h(0):                2295104*2048=3D4700372992
READ TRACK INFORMATION[#1]:
 Track State:           complete
 Track Start Address:   0*2KB
 Free Blocks:           0*2KB
 Track Size:            2295104*2KB
=46ABRICATED TOC:
 Track#1  :             14@0
 Track#AA :             14@2295104
 Multi-session Info:    #1@0
READ CAPACITY:          2295104*2048=3D4700372992

niess@stingray /tmp $ uname -a
Linux stingray 2.6.19 #6 PREEMPT Fri Dec 1 22:43:51 CET 2006 i686 Intel(R)=
=20
Pentium(R) 4 CPU 2.40GHz GNU/Linux

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