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Old 02-13-2019, 09:41 AM   #1
marcellinus
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Will adding disks to vg help performance in a life system?


Hello,

We have a large db server with lots of iowaits (100% busy) on the dbvg.
I was wondering if adding pv's to the dbvg will help.
Will LVM start distibuting the lv data to the new disks online?

Regards, Marcel
 
Old 02-13-2019, 11:54 AM   #2
MensaWater
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By default it doesn't redistribute existing extents. If your LV was created with striping it would balance but on a quick search it appears you can't change the existing linear (extents all on one PV) to striped. You could:
1) Backup everything in the filesystem(s) on the LV(s) now.
2) Unmount the filesystem(s) on the LV(s)
2) Blow away the LV(s)
3) vgextend the Volume Group to add the new disk (ideally same size as the existing)
4) Recreate the LVs using striping so it spreads across the 2 disks/PVs.
5) Recreate the filesystem(s) on the recreated LV(s)
6) Restore the backup to the recreated filesystem(s)

You don't say what kind of storage you're using. Are these internal disks? Are you using a hardware RAID controller or software (metadisk) RAID? SAN disks?

It may be the iowait you're seeing is because of poor performance via an internal RAID or SAN adapter and if so adding another disk or LUN to the same adapter might not help.

If you only have 1 physical disk (or 2 physical disks with LV striping) the failure of a single disk loses all your data. Hopefully you're doing regular backups.
 
Old 02-13-2019, 12:25 PM   #3
pan64
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probably helps: https://www.ibm.com/support/knowledg...sk_io_perf.htm
 
Old 02-14-2019, 03:07 AM   #4
marcellinus
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My storage is coming from an EMC Compellent (SSD pinned now) , via HBA's connected to an ESX server, provided as luns to a VM. 3 luns of 2 TB each
Rhel 7.6
Maybe it is the way the luns on VMWare were created. I will have a talk with the VM admin.

Thanks for the info .
 
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Old 02-14-2019, 03:35 AM   #5
syg00
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Did you bother to search this ?. A simple search on "EMC compellent" (not latency or anything related), returned this as the very first hit.
 
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Old 02-14-2019, 08:49 AM   #6
MensaWater
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Quote:
Originally Posted by pan64 View Post
The mention of smitty in that suggests it is related to AIX rather than Linux. LVM on HP-UX and AIX are somewhat similar to the one on Linux but not exactly the same.
 
Old 02-14-2019, 12:08 PM   #7
pan64
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Quote:
Originally Posted by MensaWater View Post
The mention of smitty in that suggests it is related to AIX rather than Linux. LVM on HP-UX and AIX are somewhat similar to the one on Linux but not exactly the same.
Yes, I know that. But actually there were some tips which could be used to find the reason. At least I thought that.
 
  


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