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10 zonefs is a very simple file system exposing each zone of a zoned block device
11 as a file. Unlike a regular POSIX-compliant file system with native zoned block
17 As such, zonefs is in essence closer to a raw block device access interface
18 than to a full-featured POSIX file system. The goal of zonefs is to simplify
20 raw block device file accesses with a richer file API, avoiding relying on
24 by allowing SSTables to be stored in a zone file similarly to a regular file
25 system rather than as a range of sectors of the entire disk. The introduction
33 Zoned storage devices belong to a class of storage devices with an address
34 space that is divided into zones. A zone is a group of consecutive LBAs and all
38 conventional zones. Any read or write access can be executed, similarly to a
41 sequentially. Each sequential zone has a write pointer maintained by the
43 to the device. As a result of this write constraint, LBAs in a sequential zone
44 cannot be overwritten. Sequential zones must first be erased using a special
52 Solid State Disks (SSD) storage devices can also implement a zoned interface
54 The NVMe Zoned NameSpace (ZNS) is a technical proposal of the NVMe standard
55 committee aiming at adding a zoned storage interface to the NVMe protocol.
60 Zonefs exposes the zones of a zoned block device as files. The files
70 persistently stores a magic number and optional feature flags and values. On
72 and populates the mount point with a static file tree solely based on this
77 device storing the super block is never exposed as a zone file by zonefs. If
78 the zone containing the super block is a sequential zone, the mkzonefs format
79 tool always "finishes" the zone, that is, it transitions the zone to a full
90 the device only has a single conventional zone at sector 0, the zone will not
91 be exposed as a file as it will be used to store the zonefs super block. For
108 of zones of a particular type. That is, both the "cnv" and "seq" directories
119 The number of blocks of a file as reported by stat() and fstat() indicates the
140 attempt at accepting random writes and will fail any write request that has a
144 Since dirty page writeback by the page cache does not guarantee a sequential
168 aggregated into a single larger file instead of the default one file per zone.
181 * A zone may transition to the read-only condition (BLK_ZONE_COND_READONLY):
184 read/write access) can change the zone condition back to a normal read/write
185 state. While the reasons for the device to transition a zone to read-only
186 state are not defined by the standards, a typical cause for such transition
187 would be a defective write head on an HDD (all zones under this head are
190 * A zone may transition to the offline condition (BLK_ZONE_COND_OFFLINE):
193 transitions, the reasons for a drive to transition a zone to the offline
194 condition are undefined. A typical cause would be a defective read-write head
199 requests with a start sector that does not correspond to a zone write pointer
202 may still happen in the case of a partial failure of a very large direct I/O
212 errors can propagate through a stream of cached sequential data for a zone
222 but only if the file zone is still in a good condition and there is no
224 If a problem is detected, I/O error recovery is executed (see below table).
228 * A zone condition change to read-only or offline also always triggers zonefs
231 Zonefs minimal I/O error recovery may change a file size and file access
235 Immediate or delayed write errors in a sequential zone file may cause the file
237 the file zone. For instance, the partial failure of a multi-BIO large write
243 A file size may also be reduced to reflect a delayed write error detected on
250 A zone condition change to read-only is indicated with a change in the file
292 with mkfs.zonefs (mkzonefs) will not change back offline zone files to a good
298 zone-offline mount options are temporary for zones in a good condition.
302 actions, that is, file size fixes for zones in a good condition. Zones
321 If a read-only zone is found at mount time, the zone is always treated in the
325 discover the amount of data that has been written to the zone. In the case of a
329 A zoned block device (e.g. an NVMe Zoned Namespace device) may have limits on
332 translates into a risk for applications to see write IO errors due to this
333 limit being exceeded if the zone of a file is not already active when a write
337 to be made active using an open zone command when a file is opened for writing
340 "explicit-open" mount option will result in a zone close command being issued
341 to the device on the last close() of a zone file if the zone is not full nor
352 zonefs-tools also includes a test suite which can be run against any zoned
358 The following formats a 15TB host-managed SMR HDD with 256 MB zones
365 dr-xr-xr-x 2 root root 1 Nov 25 13:23 cnv
366 dr-xr-xr-x 2 root root 55356 Nov 25 13:23 seq
370 conventional zone file (all conventional zones are aggregated under a single
375 -rw-r----- 1 root root 140391743488 Nov 25 13:23 0
377 This aggregated conventional zone file can be used as a regular file::
387 -rw-r----- 1 root root 0 Nov 25 13:23 0
388 -rw-r----- 1 root root 0 Nov 25 13:23 1
389 -rw-r----- 1 root root 0 Nov 25 13:23 2
391 -rw-r----- 1 root root 0 Nov 25 13:23 55354
392 -rw-r----- 1 root root 0 Nov 25 13:23 55355
403 -rw-r----- 1 root root 4096 Nov 25 13:23 /mnt/seq/0
410 -rw-r----- 1 root root 268435456 Nov 25 13:49 /mnt/seq/0
417 -rw-r----- 1 root root 0 Nov 25 13:49 /mnt/seq/0
420 of a file as reported by stat() and fstat() indicates the capacity of the file
428 Access: 2019-11-25 13:23:57.048971997 +0900
429 Modify: 2019-11-25 13:52:25.553805765 +0900
430 Change: 2019-11-25 13:52:25.553805765 +0900