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 What's the difference between a pdisk and hdisk

Following AIX LVM terminology a VG is a collection of disks. A disk or
PV is represented by hdiskx. For example, hdisk0 is typically the disk
in rootvg. So what then is a pdisk or physical disk?

Carrying out the following commands only serves to confuse the issue:

# lscfg -vp pdisk0 | grep pdisk0
# pdisk0            00-05-P           4GB SSA C Physical Disk Drive

# lscfg -vp hdisk0 | grep hdisk0
# hdisk0            00-07-A1-3,0      2.2 GB 16 Bit SCSI Disk Drive

With thanks.

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 Thu, 10 Jul 2003 22:06:19 GMT   
 What's the difference between a pdisk and hdisk

if you arange 5 SSA Disks in a, for example RAID-5, then you have 5
pdisks and one hdisk.


 Fri, 11 Jul 2003 00:34:09 GMT   
 What's the difference between a pdisk and hdisk schrieb:


pdisk is a physical disk, hdisk is a logical disk

 Fri, 11 Jul 2003 00:57:34 GMT   
 What's the difference between a pdisk and hdisk
More generally:

SSA uses the "pdiskX" notation to specify a physical disk drive in the
SSA loop.  SSA RAID arrays are built using collections of pdisks and
present this collection to the AIX LVM as an hdisk.

If you do not configure your SSA disks in a RAID array, then 1 pdisk => 1
hdisk.  Note that the value of X does NOT have to be (and in most cases is
not) the same between 'pdiskX' and 'hdiskX'

To find out what pdisk is associated with a given hdisk or vice versa, you
can use the 'ssaxlate' command.

AFAIK SSA is the only thing that uses the "pdisk" nomenclature.

Scott A. Ellerman                         \ IBM Certified
Lab Administrator                          \   Advanced Technical Expert - AIX
GSM/UMTS Call Server OA&M Integration (2I38)\  Specialist - RS/6000 SP
Nortel Networks                              \ Specialist - AIX HACMP

Any opinions expressed in this message are mine alone and not those
of Decision Consultants Inc., IBM, or Nortel Networks, unless expressly
stated otherwise.

 Sat, 12 Jul 2003 00:37:43 GMT   
 What's the difference between a pdisk and hdisk
OK.  pdisks are a function of SSA arrays.  You see, with SSA, you get
*another* level of abstraction before you ever get to the LVM.  The
pdisks are the actual, real SSA disks, which the SSA array then uses to
construct virtual hdisks.  The hdisks then become the "physical volumes"
that make up the LVM's volume groups, are the partitioned to provide
the logical volumes.  lscfg should show you "hdisk"s that are "SSA Logical
Disk Drive"s.  These are the virtual hdisks created by the SSA controllers.
Your SSA utilities can tell you how your pdisks map to your hdisks;
consult your SSA manuals for more information.

                  Chris Mattern

 Sat, 12 Jul 2003 02:31:59 GMT   
   [ 5 post ] 

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