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vxvm中的几个概念我不懂
Plexes
Volume Manager uses subdisks to build virtual objects called plexes. A plex is a structured or ordered collection of subdisks that represents one copy of the data in a volume. A plex consists of one or more subdisks located on one or more physical disks.
A plex is also called a mirror. The terms plex and mirror can be used interchangeably, even though a plex is only one copy of the data. The terms "mirrored" or "mirroring" imply two or more copies of data.
The length of a plex is determined by the last block that can be read or written on the last subdisk in the plex.
The default naming convention for plexes in a volume is volumename-##. The default plex name consists of the volume name, a hyphen, and a two-digit number.
Plex Types
Plexes can be categorized into three types:
Complete plex: A complete plex holds a complete copy of a volume and therefore maps the entire address space of the volume. A volume must have at least one complete plex. Most plexes in VxVM are complete plexes. For example, if a volume is 1 MB in length, then the complete plex must also be at least 1 MB in length, and the 1 MB of address space must be mapped to one or more subdisks whose combined length adds up to 1 MB with no gaps in the address space.
Sparse plex: A sparse plex is a plex that has a length that is less than the length of the volume or that maps to only part of the address space of a volume. Sparse plexes are primarily used for performance improvement. For example, a sparse plex can be used by a RAM disk to map to a hot spot within a volume to improve read performance. The RAM disk needs to be of sufficient size and offset to cover the hot spot and does not need to map to the whole volume. Sparse plexes are not commonly used in newer VxVM versions.
Log plex: A log plex is a plex that is dedicated to logging. A log plex is used to speed up data consistency checks and repairs after a system failure. RAID-5 and mirrored volumes typically use a log plex.
A volume must have at least one complete plex that has a complete copy of the data in the volume with at least one associated subdisk. Other plexes in the volume can be complete, sparse, or log plexes. A volume can have up to 32 plexes; however, you should never use more than 31 plexes in a single volume. Volume Manager requires one plex for automatic or temporary online operations |
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