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72 lines
2.9 KiB
Plaintext
72 lines
2.9 KiB
Plaintext
lvconvert changes the LV type and includes utilities for LV data
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maintenance. The LV type controls data layout and redundancy.
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The LV type is also called the segment type or segtype.
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.P
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To display the current LV type, run the command:
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.P
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.B lvs -o name,segtype
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.I LV
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.P
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In some cases, an LV is a single device mapper (dm) layer above physical
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devices. In other cases, hidden LVs (dm devices) are layered between the
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visible LV and physical devices. LVs in the middle layers are called sub LVs.
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A command run on a visible LV sometimes operates on a sub LV rather than
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the specified LV. In other cases, a sub LV must be specified directly on
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the command line.
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.P
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Sub LVs can be displayed with the command:
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.P
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.B lvs -a
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.P
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The
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.B linear
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type is equivalent to the
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.B striped
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type when one stripe exists.
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In that case, the types can sometimes be used interchangeably.
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.P
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In most cases, the
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.B mirror
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type is deprecated and the
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.B raid1
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type should be used. They are both implementations of mirroring.
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.P
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Striped raid types are
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\fBraid0/raid0_meta\fP,
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\fBraid5\fP (an alias for raid5_ls),
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\fBraid6\fP (an alias for raid6_zr) and
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\fBraid10\fP (an alias for raid10_near).
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.P
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As opposed to mirroring, raid5 and raid6 stripe data and calculate parity
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blocks. The parity blocks can be used for data block recovery in case
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devices fail. A maximum number of one device in a raid5 LV may fail, and
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two in case of raid6. Striped raid types typically rotate the parity and
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data blocks for performance reasons, thus avoiding contention on a single
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device. Specific arrangements of parity and data blocks (layouts) can be
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used to optimize I/O performance, or to convert between raid levels. See
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\fBlvmraid\fP(7) for more information.
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.P
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Layouts of raid5 rotating parity blocks can be: left-asymmetric
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(raid5_la), left-symmetric (raid5_ls with alias raid5), right-asymmetric
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(raid5_ra), right-symmetric (raid5_rs) and raid5_n, which doesn't rotate
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parity blocks. Layouts of raid6 are: zero-restart (raid6_zr with alias
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raid6), next-restart (raid6_nr), and next-continue (raid6_nc).
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.P
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Layouts including _n allow for conversion between raid levels (raid5_n to
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raid6 or raid5_n to striped/raid0/raid0_meta). Additionally, special raid6
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layouts for raid level conversions between raid5 and raid6 are:
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raid6_ls_6, raid6_rs_6, raid6_la_6 and raid6_ra_6. Those correspond to
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their raid5 counterparts (e.g. raid5_rs can be directly converted to
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raid6_rs_6 and vice-versa).
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.P
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raid10 (an alias for raid10_near) is currently limited to one data copy
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and even number of sub LVs. This is a mirror group layout, thus a single
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sub LV may fail per mirror group without data loss.
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.P
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Striped raid types support converting the layout, their stripesize and
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their number of stripes.
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.P
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The striped raid types combined with raid1 allow for conversion from
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linear \[->] striped/raid0/raid0_meta and vice-versa by e.g. linear \[<>] raid1
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\[<>] raid5_n (then adding stripes) \[<>] striped/raid0/raid0_meta.
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