How to determine the OS header block for the raw device

[Oliver Tian]

I plan to use the dd command to backup the Oracle 10g RAC database files which are on the raw logical volumes - /dev/vg20/rlvol01 ...

How I can determine the OS header block for the raw device /dev/vg20/rlvol01? when setting the skip=n in dd command.

Here is the command provided by Oracle support:

dd if=/dev/vg20/rlvol01 of=/backup/dbfile1.dbf bs=8192 skip=??? <-- How to determine

--- Volume groups ---
VG Name /dev/vg20
VG Write Access read/write
VG Status available, shared, client
Max LV 255
Cur LV 9
Open LV 9
Max PV 16
Cur PV 1
Act PV 1
Max PE per PV 12799
VGDA 2
PE Size (Mbytes) 4
Total PE 12797
Alloc PE 5111
Free PE 7686
Total PVG 0
Total Spare PVs 0
Total Spare PVs in use 0

--- ---

hqsfd10 Server
hqjsdsp1 Client
hqjsdsp2 Client

--- Logical volumes ---
LV Name /dev/vg20/rac1_system_raw_512m
LV Status available/syncd
LV Size (Mbytes) 512
Current LE 128
Allocated PE 128
Used PV 1




Thanks in advance!

[A. Clay Stephenson · Accepted solution]

There is no OS header in an HP-UX raw volume. Just leave off the skip parameter entirely.

[A. Clay Stephenson]

I would also set bs higher than 8k (regardless of your DB block size). I would bump it up to at least 64k and 256K would be better still.

[Navin Bhat_2]

skip=0

[Sanjay_6]

Hi,

What header blocks?

Everything on the lv is data. if it is raw lv, the rlv is what you want to back up. You don't need a skip with the dd command.

Hope this helps.

Regds

[Oliver Tian]

Now I like to ask the question in the reversed direction - Copying filesystem to raw device.

dd if=/backup/dbfile.dbf of=/dev/vg20/rlvol01 bs=8192 seek=??? <-- How to determine

Thanks.

[A. Clay Stephenson]

Same answer. There is no header. No skip, no seek, and performance is going to be a dog unless you increase that bs=8192 to something like bs=256k. On OS's that do have volume headers, you hade to use a small bs because count, skip, and seek are based upon bs but since you won't be skipping, seeking, or counting, you are free to increase bs -- and again, it doesn't matter that your database block size might be 8k.

[Navin Bhat_2]

You do not need iseek or skip in either direction. Refer to metalink doc id 25067.996