AIX

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:

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.

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.

Dear my senario is that i have a rootvg mirrored with hdisk0 and hdisk1

now i can't increase the file system for any lv becouse the region in hdisk0 is diffrent of hdisk1 , is there any way to make the region of the LV in hdisk0 same as hdisk1 .

Yes: remove the mirror of all the LVs so that the (used space of the) VG is on one disk only. Start a "reorgvg rootvg" then to rearrange all the LVs to be contiguous again. Once this is finished remirror the LVs again using the freed disk. The LVM should make the placement identical on the disk. If you are not satisfied with the result you can also create and use map files (see the man page of "mklv") to control the process.

I hope this helps.

bakunin