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

[Eli Malul]

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 at 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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