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Old 04-10-2012, 02:50 AM   #1
sluge
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Question LVM mirror also mirrored log, why?


Hello
I found that LVM has a new feature, it can mirror not only data, but log also. Why? Is log data is so important? It will be regenerated if disk fails.
 
Old 04-10-2012, 07:54 AM   #2
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At a guess: Performance. If you have data important enough to mirror it may be it is also important enough that you don't want to wasted time in regenerating log info to get the LVs back online.
 
Old 04-10-2012, 01:39 PM   #3
Satyaveer Arya
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LVM mirroring at a minimum requires 3 physical volumes.

2 volumes for the both sides of the mirror and a volume for log.

The way mirroring works in LVM is that the system creates arbitrary data blocks(e.g. 512 KB in size) and it's these individual blocks that are kept in sync across the drives. The log is the essential mechanism for the system to keep the data of sync status in across reboots, hence it can't be on any of the mirrored drives. You can also configure the system to keep the log in the RAM, but this means that your drives will have to be synced every time your system's rebooted (which's a VERY bad idea, because syncing is among the slowest LVM/RAID operations ever).
 
Old 04-10-2012, 11:52 PM   #4
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[QUOTE=Satyaveer Arya;4649508]LVM mirroring at a minimum requires 3 physical volumes.

In RHEL you can use at minimum 2 PVs
 
Old 04-11-2012, 11:39 AM   #5
Satyaveer Arya
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Exactly you can take 2 PVs, it will work but in my last post I also mentioned about the another PV i.e., for log.
 
  


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