Solaris Volume Manager (SVM): Best Practices for Creation and Implementation of Soft Partitions
Last updated on NOVEMBER 03, 2016
Applies to:Solstice DiskSuite Software - Version 4.2.1 to 4.2.1 [Release 4.0]
Sun Solaris Volume Manager (SVM) - Version 11.9.0 to 11.11 [Release 11.0]
Information in this document applies to any platform.
Solaris Volume Manager (SVM) was originally implemented to allow creation of software RAID devices from disk drives or LUNs. These RAID devices (or metadevices) were created from physical partitions on the disk. You could combine physical disk partitions into stripes or concatentions, mirrors and RAID-5 metadevices.
A limitation existed in that a disk can only have 8 partitions, thus limiting the number of metadevices to 8 per disk. This may have originally been an acceptable limitation, but as disk sizes increased, the restriction became unmanageable.
This is where soft partitions come into play. Soft partitioning allows a disk to be subdivided into many partitions which are controlled and maintained by SVM, thereby removing the 8-metadevice limitation per disk.
A soft partition is made up of one or more "extents." Each extent is preceded by an extent header, which is a consistency record that contains such information as the metadevice (soft partition) name, its status, size, and a checksum. Each extent header is 1 block (512 bytes) in size.
Soft partition configuration information is written in two places:
- the state database replicas;
- directly onto the disk, in the extent header.
Extent headers are also referred to as watermarks and are used in administration and recovery.
Several more points of interest:
Soft partitioning was introduced in Solaris 8 with SVM product patch 108693-06.
Soft partitions are managed with the md_sp kernel driver.
228 78328000 4743 - 1 md_sp (Meta disk soft partition module)
There are new options to the metainit command. The -p option means that the command refers to soft partitions.
# metainit softpart -p component -o offset -b size
The metattach command now allows for growing soft partitions.
There is a new command, metarecover, to administer the extents on a disk.
Do not use soft partitions unless you plan on making more than 8 metadevices from a disk drive. They serve no purpose and introduce a new layer of complexity.
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