docs/devel/zoned-storage.rst

2 zoned-storage
5 Zoned Block Devices (ZBDs) divide the LBA space into block regions called zones
10 https://zonedstorage.io/docs/introduction/zoned-storage
12 1. Block layer APIs for zoned storage
13 -------------------------------------
14 QEMU block layer supports three zoned storage models:
15 - BLK_Z_HM: The host-managed zoned model only allows sequential writes access
16 to zones. It supports ZBD-specific I/O commands that can be used by a host to
18 - BLK_Z_HA: The host-aware zoned model allows random write operations in
19 zones, making it backward compatible with regular block devices.
20 - BLK_Z_NONE: The non-zoned model has no zones support. It includes both
21 regular and drive-managed ZBD devices. ZBD-specific I/O commands are not
24 The block device information resides inside BlockDriverState. QEMU uses
26 block layer while processing I/O requests. A BlockBackend has a root pointer to
27 a BlockDriverState graph(for example, raw format on top of file-posix). The
29 the way up to the BlockBackend. If the zoned storage model in file-posix is
30 set to BLK_Z_HM, then block drivers will declare support for zoned host device.
32 The block layer APIs support commands needed for zoned storage devices,
36 --------------------------------------
38 like the virtio-blk emulation or the qemu-io-cmds.c utility can use block layer
41 For example, to test zone_report on a null_blk device using qemu-io is::
43   $ path/to/qemu-io --image-opts -n driver=host_device,filename=/dev/nullb0 -c "zrp offset nr_zones"
45 To expose the host's zoned block device through virtio-blk, the command line
46 can be (includes the -device parameter)::
48   -blockdev node-name=drive0,driver=host_device,filename=/dev/nullb0,cache.direct=on \
49   -device virtio-blk-pci,drive=drive0
51 Or only use the -drive parameter::
53   -driver driver=host_device,file=/dev/nullb0,if=virtio,cache.direct=on
56 (1) Using virtio-scsi: --device scsi-block allows for the passing through of
58 (2) PCI device pass-through: While NVMe ZNS emulation is available for testing