Position of the logical volume on the physical volume | Unix Linux Forums | AIX

  Go Back    


AIX AIX is IBM's industry-leading UNIX operating system that meets the demands of applications that businesses rely upon in today's marketplace.

Position of the logical volume on the physical volume

AIX


Tags
aix, unix

Closed Thread    
 
Thread Tools Search this Thread Display Modes
    #1  
Old 01-04-2013
adilyos's Avatar
adilyos adilyos is offline
Registered User
 
Join Date: Jan 2012
Last Activity: 31 July 2013, 8:28 AM EDT
Posts: 53
Thanks: 0
Thanked 0 Times in 0 Posts
Position of the logical volume on the physical volume

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
Sponsored Links
    #2  
Old 01-04-2013
kah00na's Avatar
kah00na kah00na is offline
Registered User
 
Join Date: Jul 2007
Last Activity: 15 October 2014, 11:26 AM EDT
Location: Kansas
Posts: 298
Thanks: 21
Thanked 26 Times in 21 Posts
In smitty when you are creating a LV, you'll see:

Code:
POSITION on physical volume                         middle

You can change this to whatever you want. If you are using a SAN though, it probably won't make any difference since most modern SANs move data around as needed and spread it across multiple disks all unknown to the OS. If you are using internal physical disks, you will most likely see a difference - outer is faster than the inner because the head that reads the disk can read more on the outer edge because more disk is passed under it in a single disk rotation.
Sponsored Links
    #3  
Old 01-04-2013
zxmaus's Avatar
zxmaus zxmaus is offline Forum Advisor  
Event Manager
 
Join Date: May 2008
Last Activity: 7 September 2014, 5:24 AM EDT
Location: in a putty session :)
Posts: 811
Thanks: 19
Thanked 70 Times in 62 Posts
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
    #4  
Old 01-04-2013
kah00na's Avatar
kah00na kah00na is offline
Registered User
 
Join Date: Jul 2007
Last Activity: 15 October 2014, 11:26 AM EDT
Location: Kansas
Posts: 298
Thanks: 21
Thanked 26 Times in 21 Posts
Quote:
Originally Posted by zxmaus View Post
the center is the fastest on a disk...
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
Sponsored Links
    #5  
Old 01-04-2013
zxmaus's Avatar
zxmaus zxmaus is offline Forum Advisor  
Event Manager
 
Join Date: May 2008
Last Activity: 7 September 2014, 5:24 AM EDT
Location: in a putty session :)
Posts: 811
Thanks: 19
Thanked 70 Times in 62 Posts
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.
Sponsored Links
    #6  
Old 01-04-2013
kah00na's Avatar
kah00na kah00na is offline
Registered User
 
Join Date: Jul 2007
Last Activity: 15 October 2014, 11:26 AM EDT
Location: Kansas
Posts: 298
Thanks: 21
Thanked 26 Times in 21 Posts
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.
Sponsored Links
    #7  
Old 01-05-2013
MichaelFelt MichaelFelt is offline
Registered User
 
Join Date: Nov 2012
Last Activity: 11 December 2013, 7:33 AM EST
Location: on the road for work; home is private time
Posts: 311
Thanks: 6
Thanked 76 Times in 71 Posts
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


Code:
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


Code:
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

This looks "bad" or less than ideal - 0% and in two regions - however, in physical terms it is a sequential as it gets. A simple command will improve the 0% to >50% (see below).


Code:
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

Here, I can see the logical volume is organized sequentially - starting in the center region, and proceeding into the "inner middle" region as one long sequence.

Now to get better stats I can do the following:
(change the preferred region to center from middle)


Code:
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

Hope this helps!
Sponsored Links
Closed Thread

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

More UNIX and Linux Forum Topics You Might Find Helpful
Thread Thread Starter Forum Replies Last Post
Confusion Regarding Physical Volume,Volume Group,Logical Volume,Physical partition kashifsd17 UNIX for Dummies Questions & Answers 6 07-06-2012 05:19 PM
Logical volume name conflict in two volume group dantares AIX 10 12-07-2009 01:12 PM
Unmount and remove all Logical vol.Volume group and physical disk joeli HP-UX 3 01-27-2009 10:59 AM
Basic Filesystem / Physical Volume / Logical Volume Check chipahoys AIX 1 12-02-2008 08:05 AM
LVM - Extending Logical Volume within Volume Group ghimanshu UNIX for Advanced & Expert Users 3 07-26-2007 08:39 AM



All times are GMT -4. The time now is 07:25 PM.