docs/interop/qcow2.txt

4 (host) clusters. A cluster is the unit in which all allocations are done,
8 clusters of the same size.
39                     Must not be less than 9 (i.e. 512 byte clusters).
46                     must be at least 14 (i.e. 16384 byte clusters).
58                     (56 bits) of populated clusters, and an image may
79                     Number of clusters that the refcount table occupies
107                                 external data file is used. Guest clusters are
109                                 images, clusters in the external data file are
112                                 guest offset and neither compressed clusters
120                                 clusters. The compression_type field must be
212                     Defines the compression method used for compressed clusters.
213                     All compressed clusters in an image use the same compression
226                     <https://www.zlib.net/> in QEMU. However, clusters with the
356 The first 592 bytes of the header clusters will contain the LUKS
373 to the start of the LUKS header clusters in the qcow2 container,
438 qcow2 manages the allocation of host clusters by maintaining a reference count
445 refcount table can cover multiple clusters, however it needs to be contiguous
451 Although a large enough refcount table can reserve clusters past 64 PB
454 to clusters prior to that point.
495 guest clusters to host clusters. They are called L1 and L2 table.
498 clusters, however it must be contiguous in the image file. L2 tables are
508 compressed clusters to reside below 512 TB (49 bits), and this limit
532                     offset is 0, the L2 table and all clusters described by this
545               62:   0 for standard clusters
546                     1 for compressed clusters
548               63:   0 for clusters that are unused, compressed or require COW.
549                     1 for standard clusters whose refcount is exactly one.
553                     With external data files, all guest clusters have an
556                     for all allocated clusters.
580 Compressed Clusters Descriptor (x = 62 - (cluster_bits - 8)):
609 In these images standard data clusters are divided into 32 subclusters of the
612 indicating the status of each one of them. Compressed data clusters don't have
626 Subcluster Allocation Bitmap (for standard clusters):
650 Subcluster Allocation Bitmap (for compressed clusters):
653                     Compressed clusters don't have subclusters,
659 switch the active L1 table, so that a different set of host clusters are
663 L2 tables and clusters reachable from this L1 table must be increased, so that
824                     Extra data must never contain references to clusters or in
825                     some other way allocate additional clusters.
839 structures like for refcounts and guest clusters mapping) for the mapping of
840 bitmap data to host clusters. This structure is called the bitmap table.
843 and may use multiple clusters, however, it must be contiguous in the image
865 As noted above, bitmap data is stored in separate clusters, described by the