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Working set caching for virtual images in a cloud environment Disclosure Number: IPCOM000209875D
Publication Date: 2011-Aug-18
Document File: 3 page(s) / 41K

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The Prior Art Database


Here is disclosed a method to cache locally sectors of an hard disk, used as a reference image, togheter with the modified disk sectors.

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Working set caching for virtual images in a cloud environment

A cloud virtual infrastructure usually hosts many virtual machines (VMs) that have a very similar configuration and set of managed data. To optimize the use of storage and speed-up the provisioning process for those VMs, it is possible to boot the VM from a remote, shared, disk volume that will be common to a large number of VMs. The differences between the various VMs can be stored in a VM specific, non shared volume that captures all the write operations performed by the associated VM. So the common status is kept in the shared volume, while the differences between the VMs are maintained in some VM private storage. This approach has one major drawback: if a VM must access multiple times the common data, these data will be transferred multiple times trough the network, from the shared volume, for example using the iSCSI protocol.

Many solutions have been proposed to solve this problem, like storing the data read from the shared volume in the private volume, so that the VM will have to read the data from the network only once, and then the data will be available locally.

This solution has the drawback of requiring, for each VM, a private volume that is as large as the shared one, thus completing losing the space optimization deriving from keeping the shared data in a shared volume.

The solution which is proposed leverages the free space in the private volume to optimize the network data transfer. This way, space that would be otherwise wasted, gets used to cache locally data previously read through the network.

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The space used for the read cache changes during the life of the VM, because, as the amount of private data increases, the read cache space gets reduced. This is not a real drawback, because the total size of the volume can be calculated considering the expected size of the

private data set for a VM, plus the required cache size to obtain an...