The uberblock version is incremented whenever an incompatible on-disk format change is made to the SPA, DMU, or ZAP. More...

Collaboration diagram for uberblock:

Data Fields
uint64_t	ub_magic
	UBERBLOCK_MAGIC.
uint64_t	ub_version
	SPA_VERSION.
uint64_t	ub_txg
	txg of last sync
uint64_t	ub_guid_sum
	sum of all vdev guids
uint64_t	ub_timestamp
	UTC time of last sync.
blkptr_t	ub_rootbp
	MOS objset_phys_t.
uint64_t	ub_software_version
	highest SPA_VERSION supported by software that wrote this txg

Detailed Description

The uberblock version is incremented whenever an incompatible on-disk format change is made to the SPA, DMU, or ZAP.

Note:: The first two fields should never be moved. When a storage pool is opened, the uberblock must be read off the disk before the version can be checked. If the ub_version field is moved, we may not detect version mismatch. If the ub_magic field is moved, applications that expect the magic number in the first word won't work.

Definition at line 48 of file uberblock_impl.h.