Alberto García

O Grove (Spain)

One of the founding members of Igalia, Alberto loves computing since he got his first ZX Spectrum in the early nineties.

Latest Updates

Alberto García 16/11/2017

“Improving the performance of the qcow2 format” at KVM Forum 2017

I was in Prague last month for the 2017 edition of the KVM Forum. There I gave a talk about some of the work that I’ve been doing this year to improve the qcow2 file format used by QEMU for storing disk images. The focus of my work is to make qcow2...

Alberto García 08/02/2017

QEMU and the qcow2 metadata checks

When choosing a disk image format for your virtual machine one of the factors to take into considerations is its I/O performance. In this post I’ll talk a bit about the internals of qcow2 and about one of the aspects that can affect its performance...

Alberto García 24/05/2016

I/O bursts with QEMU 2.6

QEMU 2.6 was released a few days ago. One new feature that I have been working on is the new way to configure I/O limits in disk drives to allow bursts and increase the responsiveness of the virtual machine. In this post I’ll try to explain how it...

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qcow2: Fix Coverity warning when calculating the refcount cache size

qcow2: Fix Coverity warning when calculating the refcount cache size MIN_REFCOUNT_CACHE_SIZE is 4 and the cluster size is guaranteed to be at most 2MB, so the minimum refcount cache size (in bytes) is always going to fit in a 32-bit integer. Coverity...

Alberto García31/05/2018

docs: Document the new default sizes of the qcow2 caches

docs: Document the new default sizes of the qcow2 caches We have just reduced the refcount cache size to the minimum unless the user explicitly requests a larger one, so we have to update the documentation to reflect this change. Signed-off-by:...

Alberto García15/05/2018

qcow2: Give the refcount cache the minimum possible size by default

qcow2: Give the refcount cache the minimum possible size by default The L2 and refcount caches have default sizes that can be overridden using the l2-cache-size and refcount-cache-size (an additional parameter named cache-size sets the combined size of...

Alberto García15/05/2018

specs/qcow2: Clarify that compressed clusters have the COPIED bit reset

specs/qcow2: Clarify that compressed clusters have the COPIED bit reset Compressed clusters are not supposed to have the COPIED bit set, but this is not made explicit in the specs, so let's document it. Signed-off-by: Alberto Garcia Message-id:...

Alberto García15/05/2018

Fix error message about compressed clusters with OFLAG_COPIED

Fix error message about compressed clusters with OFLAG_COPIED Compressed clusters are not supposed to have the COPIED bit set. "qemu-img check" detects that and prints an error message reporting the number of the affected host cluster. This doesn't...

Alberto García15/05/2018