From: Kurt Freydl (kf@leuthold-partner.ch)
Date: Wed Oct 30 2002 - 02:08:36 EST
Hi Admins,
Thank you very much !
QUESTION:
On a B2000 with 2x36GB Disks I have installed HP-UX 10.20.
I've increased the physical extents from 4MB to 64MB, because
with 4MB it wasn't possible to use a 36GB Disk as boot disk.
Next I want to install MirrorDisk.
Question: Are there any disadvantages (ex. performance with mirror)
whith physical extents greater than the default value (4MB) ?
What's your advice.
ANSWERS:
Eef Hartman:
> On a B2000 with 2x36GB Disks I have installed HP-UX 10.20.
> I've increased the physical extents from 4MB to 64MB, because
> with 4MB it wasn't possible to use a 36GB Disk as boot disk.
Even with that trick all of the "boot files", that is: most of /stand,
will have to stay within the first 4 GB of the disk. The actual boot CODE
(in the firmware) isn't capable of handling physical BLOCKS (not extends,
for the boot code the addresses are recalculated in physical block numbers)
over the 32-bit limit (4 GB).
> Next I want to install MirrorDisk.
>
> Question: Are there any disadvantages (ex. performance with mirror)
> whith physical extents greater than the default value (4MB) ?
Except for granularity (all volumes will have to be a multiple of 64 MB,
so you cannot have i.e. a 16 or 32 MB "/stand" volume anymore), no.
The PE is only used for the LVM mapping itself, not for the underlying
file systems. It might even be faster then with the lower PE size.
Bill Hassell:
A physical extent is simply a mapping technique for LVM and 4Mb versus 64Mb
has no effect other than making small lvols an even multiple of 64Mb. When the
extents are assigned in order (not striped across several disks), the extent
size has no performance impact.
BTW: 36Gb is really small. You could keep 4Mb extents and just increase the
max number of extents for the volume group (vgcreate or SAM option)
Thank you for response :-)
Kurt
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leuthold + partner ag fax: +41 (0)52 269 07 79
Technikumstrasse 38 e-mail: mailto:kf@leuthold-partner.ch
CH-8400 Winterthur Switzerland
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