[linux-lvm] Question, what is the first 384 cyclinder in the PV?

[linux-lvm] Question, what is the first 384 cyclinder in the PV?

[Jewsco Pius Jacquez]

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Hello,

Any idea what is the first 512bytes 384 cylinder of a PV is designed or used for?
Can an ordinary application use it?

Thanks,
jewsco

This message and the information contained herein is proprietary and confidential and subject to the Amdocs policy statement,
you may review at http://www.amdocs.com/email_disclaimer.asp

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Re: [linux-lvm] Question, what is the first 384 cyclinder in the PV?

[Jewsco Pius Jacquez]

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I'm sorry, I mean the first 384 sector.

I am using RHEL5.6 kernel 2.6.18-238.12.1.el5 and have  lvm2-2.02.74-5.el5. Here is my lvm.conf.
Can an application data exist here? Like oracle data..
For instance, if I dd out from a PV with bs=512 and count=384 and I saw oracle data on it, is this ok?


Thanks,
Jewsco




From: Jewsco Pius Jacquez
Sent: Friday, July 29, 2011 11:13 AM
To: 'linux-lvm@redhat.com'
Subject: Question, what is the first 384 cyclinder in the PV?

Hello,

Any idea what is the first 512bytes 384 cylinder of a PV is designed or used for?
Can an ordinary application use it?

Thanks,
jewsco

This message and the information contained herein is proprietary and confidential and subject to the Amdocs policy statement,
you may review at http://www.amdocs.com/email_disclaimer.asp

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Re: [linux-lvm] Question, what is the first 384 cyclinder in the PV?

[Jewsco Pius Jacquez]

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Forgot to attached. Here it is..

Thanks,
Jewsco

From: Jewsco Pius Jacquez
Sent: Friday, July 29, 2011 12:36 PM
To: 'linux-lvm@redhat.com'
Subject: RE: Question, what is the first 384 cyclinder in the PV?

I'm sorry, I mean the first 384 sector.

I am using RHEL5.6 kernel 2.6.18-238.12.1.el5 and have  lvm2-2.02.74-5.el5. Here is my lvm.conf.
Can an application data exist here? Like oracle data..
For instance, if I dd out from a PV with bs=512 and count=384 and I saw oracle data on it, is this ok?


Thanks,
Jewsco




From: Jewsco Pius Jacquez
Sent: Friday, July 29, 2011 11:13 AM
To: 'linux-lvm@redhat.com'
Subject: Question, what is the first 384 cyclinder in the PV?

Hello,

Any idea what is the first 512bytes 384 cylinder of a PV is designed or used for?
Can an ordinary application use it?

Thanks,
jewsco

This message and the information contained herein is proprietary and confidential and subject to the Amdocs policy statement,
you may review at http://www.amdocs.com/email_disclaimer.asp

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[-- Attachment #2: lvm.conf --]
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devices {
    dir = "/dev"
    scan = [ "/dev" ]
    preferred_names = [ "^/dev/mapper/" ]
    filter = [ "a|/dev/mpath/.*|", "a|/dev/cciss/c0d0*|", "a|/dev/sda2$|", "r|.*|" ] 
    cache_dir = "/etc/lvm/cache"
    cache_file_prefix = ""
    write_cache_state = 1
    types = [ "device-mapper", 16 ]
    sysfs_scan = 1	
    md_component_detection = 1
    ignore_suspended_devices = 0
}
log {
    verbose = 0
    syslog = 1
    overwrite = 0
    level = 0
    
    indent = 1
    command_names = 0
    prefix = "  "
}
backup {
    backup = 1
    backup_dir = "/etc/lvm/backup"
    archive = 1
    archive_dir = "/etc/lvm/archive"
    
    retain_min = 10
    retain_days = 30
}
shell {
    history_size = 100
}
global {
    library_dir = "/usr/lib64"
    
    umask = 077
    test = 0
    units = "h"
    activation = 1
    proc = "/proc"
    locking_type = 1
    fallback_to_clustered_locking = 1
    fallback_to_local_locking = 1
    locking_dir = "/var/lock/lvm"
}
activation {
    missing_stripe_filler = "/dev/ioerror"
    reserved_stack = 256
    reserved_memory = 8192
    process_priority = -18
    volume_list = [ "vg00", "vg_local", "vg_swap", "@cmil561hb.amdocs.com" ]
    mirror_region_size = 512
    mirror_log_fault_policy = "allocate"
    mirror_device_fault_policy = "remove"
}

Re: [linux-lvm] Question, what is the first 384 cyclinder in the PV?

[Bryn M. Reeves]

On 07/29/2011 06:35 PM, Jewsco Pius Jacquez wrote:
> I’m sorry, I mean the first 384 sector.

It's space reserved for lvm2 data used to manage the volume; This part of the
device contains the LVM2 label and metadata area. (it's before the first
physical extent in the volume).

> I am using RHEL5.6 kernel 2.6.18-238.12.1.el5 and have lvm2-2.02.74-5.el5. Here 
> is my lvm.conf.
> 
> Can an application data exist here? Like oracle data..

Not generally but lvm2 does not necessarily write to every location in this
region when initialising a new device so if there was existing data on the
device when pvcreate/vgcreate ran it will not have been overwritten.

> For instance, if I dd out from a PV with bs=512 and count=384 and I saw oracle 
> data on it, is this ok?

It's not possible to say with this information - has oracle been configured to
use the whole disk?

If so then that's an error but if the data you are seeing is just "stale" data
from a previous use of the device it's not going to cause any problems.

Regards,
Bryn.