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[dm-devel] FW: the mirror log is NOT kept on disk



I just saw that clean_bits is being saved to the disk and is used to update sync_bits after crash/reboot (although the default behavior is to reset all the bits hence, resync is done for each resume).

 

But I still do not understand how should I create a mapped device with dmsetup tool which wouldl survive crash/reboot.

 

Can anyone help?

 

From: Eli Malul
Sent: Sunday, March 20, 2011 6:19 PM
To: 'dm-devel redhat com'
Subject: the mirror log is NOT kept on disk

 

Hi,

 

I tried a small test where I suspended and resumed a mirrored device without IO going on.

My expectation was that the mirror set will not get re-synced but unfortunately it did.

 

According the documentation the mirror log is kept on disk when creating a mirror logical device with 'disk' log type as an input parameter.

I looked at the code and I didn't see where the sync_bits are being written to the disk or read from the disk but only the number of regions is being saved.

 

How should a mirror device survive reboots/crashes without syncing the entire mirror set?

 

BTW – another problem is that after reboot the created logical device disappears, is there an easy way to keep it persistent or should I create at each boot?

 


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