Hello everyone,

I just read that while creating a logical volume(LV) we can choose the region of the physical volume (PV) in which the LV should be created.
When I say region I mean: outer edge - outer middle - center - inner middle and inner edge.

Can anyone help me understand the utility of that possibility ? How can we do that ( example please) ?

Thank you

In smitty when you are creating a LV, you'll see:

POSITION on physical volume                         middle

the center is the fastest on a disk - obviously this works only when you don't use raid 5 or SAN - you place it while you are creating the lv - either via smitty or with -a c option

Regards
zxmaus

The center is fastest? Outer tracks would have more sectors so as the disk spins, the head is able to read more sectors in a single disk rotation, right?

---------- Post updated at 10:13 AM ---------- Previous update was at 10:06 AM ----------

Here is a descent animation of the head seeking data on Western Digital's website. It is advertising their "IntelliSeek", but it shows how the head reads data.
Western Digital

the outer edge of the disk has a faster rotational velocity than the slower inner edge and will whip around much more quickly on the outside than in the middle. However, because not all the data on the disk will be written to the outer edge as a result of the limitations of the physical placement of the data, the fastest seek times for the hard disk heads will be in the center area of the disk, where the head is most likely to pass on average.

I guess that is why UNIX gives the option of where you want the data because if you are worried about seek times, you'd want the data in the middle, if you were wanting raw speed to save a smaller number of large files, you'd be better off putting it on the outer edges... to each his own. Long live UNIX.

IMHO the problem is placement within regions based on application activity.

The basic concept you want to follow: if the access is sequential in application terms the best I/O performance is achieved when the physical I/O access is sequential.

When application I/O is random there are many different things to consider - one of them being - is the I/O still physical, or is it VMM cached, or application cached.

In short, with modern systems (assuming more than one or two disks, i.e., separate volume groups for each application's data) there is no one best place.
Assuming some physical relationship the only advice that remains is that AIX LVM mirrored logical volumes with lots of write activity may benefit from being placed on the outer edge because the VGSA - Volume Group Status Area - is on the outer edge and gets updated anytime a mirrored LP is modified.

command you should look at:
lslv - options: none, and with -l
lspv -p

michael@x054:[/home/michael]lslv lvDAV
LOGICAL VOLUME:     lvDAV                  VOLUME GROUP:   vgData
LV IDENTIFIER:      005d858f00004c0000000115722f3acc.15 PERMISSION:     read/write
VG STATE:           active/complete        LV STATE:       closed/syncd
TYPE:               jfs2                   WRITE VERIFY:   off
MAX LPs:            1024                   PP SIZE:        16 megabyte(s)
COPIES:             1                      SCHED POLICY:   parallel
LPs:                1024                   PPs:            1024
STALE PPs:          0                      BB POLICY:      relocatable
INTER-POLICY:       minimum                RELOCATABLE:    yes
INTRA-POLICY:       middle                 UPPER BOUND:    6
MOUNT POINT:        N/A                    LABEL:          None
MIRROR WRITE CONSISTENCY: on/ACTIVE                              
EACH LP COPY ON A SEPARATE PV ?: yes                                    
Serialize IO ?:     NO                                     
INFINITE RETRY:     no

michael@x054:[/home/michael]lslv -l lvDAV
lvDAV:N/A
PV                COPIES        IN BAND       DISTRIBUTION  
hdisk1            1024:000:000  0%            000:000:541:483:000

michael@x054:[/home/michael]lspv -p hdisk1 | grep lvDAV
2085-2625  used    center        lvDAV               jfs2       N/A
2626-3108  used    inner middle  lvDAV               jfs2       N/A

michael@x054:[/home/michael]chlv -a center lvDAV
0516-652 chlv: The -a parameter for IntraPolicy must be m, im, c,
        ie or e.
michael@x054:[/home/michael]chlv -a c lvDAV     
michael@x054:[/home/michael]lslv -l lvDAV
lvDAV:N/A
PV                COPIES        IN BAND       DISTRIBUTION  
hdisk1            1024:000:000  52%           000:000:541:483:000