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65 lines
2.7 KiB
Plaintext
65 lines
2.7 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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To display the current LV type, run the command:
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.B lvs \-o name,segtype
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.I LV
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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 interchangably.
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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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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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Striped raid types are
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.B raid0/raid0_meta
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,
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.B raid5
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(an alias for raid5_ls),
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.B raid6
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(an alias for raid6_zr) and
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.B raid10
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(an alias for raid10_near).
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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 devices
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fail. A maximum number of one device in a raid5 LV may fail and two in case
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of raid6. Striped raid types typically rotate the parity blocks for performance
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reasons thus avoiding contention on a single device. Layouts of raid5 rotating
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parity blocks can be one of left-asymmetric (raid5_la), left-symmetric (raid5_ls
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with alias raid5), right-asymmetric (raid5_ra), right-symmetric (raid5_rs) and raid5_n,
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which doesn't rotate parity blocks. Any \"_n\" layouts allow for conversion between
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raid levels (raid5_n -> raid6 or raid5_n -> striped/raid0/raid0_meta).
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raid6 layouts are zero-restart (raid6_zr with alias raid6), next-restart (raid6_nr),
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next-continue (raid6_nc). Additionally, special raid6 layouts for raid level conversions
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between raid5 and raid6 are raid6_ls_6, raid6_rs_6, raid6_la_6 and raid6_ra_6. Those
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correspond to their raid5 counterparts (e.g. raid5_rs can be directly converted to raid6_rs_6
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and vice-versa).
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raid10 (an alias for raid10_near) is currently limited to one data copy and even number of
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sub LVs. This is a mirror group layout thus a single sub LV may fail per mirror group
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without data loss.
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Striped raid types support converting the layout, their stripesize
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and their number of stripes.
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The striped raid types combined with raid1 allow for conversion from linear -> striped/raid0/raid0_meta
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and vice-versa by e.g. linear <-> raid1 <-> raid5_n (then adding stripes) <-> striped/raid0/raid0_meta.
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Sub LVs can be displayed with the command
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.B lvs -a
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