[dm-devel] DM above MD raid5

[Gili B]

In case anybody wondered...
Raid5 doesnt merge reads beyond chunk size,
There was an issue in my code that didnt handle split reads well.
 
Thanks
 
From: gilib123 at hotmail.com
To: dm-devel at redhat.com
Date: Tue, 11 Aug 2015 17:26:17 +0000
Subject: [dm-devel] DM above MD raid5




hi
We are devloping an md driver that does optimized virtualiztion for SSDs.
We store some metadata on the ssds.
Everything works great when working directly above the SSDs.
When we virtualize over md, we have synch isssues.
The simple test formats volume meta data on the md.
Then unload the module and reload.
We try to read back the volume, but the checksomes comes back bad.
 
If I repeat the operation a few more times,(just the part that tries to read back the meta data),
It is finally ends up succesfully. and from there on it is always successfull.
I figured there's some sort of cache that needs to be flushed..
I tried flushing the md, flushing every write, nothing solved the issue.
 
Any help greatly apreciated.
Thanks
-Gili 
 		 	   		  

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