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Re: [Qemu-block] callout to *file in bdrv_co_get_block_status

From: Paolo Bonzini
Subject: Re: [Qemu-block] callout to *file in bdrv_co_get_block_status
Date: Fri, 17 Mar 2017 12:16:22 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 17/03/2017 12:11, Peter Lieven wrote:
>>> like VMDK or QCOW2 shouldn't we trust the information from the l2 tables in 
>>> the VMDK or QCOW2?
>> It provides additional information, for example it works better with
>> prealloc=metadata.
> Okay, understood. Can you imagine of a away to conditionally avoid this 
> second callout? In my case we have an additional
> lseek for each cluster. For a 20GB file this are approx. 327k calls to lseek. 
> And if the file has no preallocated metadata
> it will likely not improve anything. And even if the metadata is prealloced 
> what is the allocation status of the clusters?

If the metadata is preallocated, cluster will (or should) show up as
zero, speeding up the copy.


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