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lvconvert changes the LV type and includes utilities for LV data
maintenance. The LV type controls data layout and redundancy.
The LV type is also called the segment type or segtype.
To display the current LV type, run the command:
.B lvs \-o name,segtype
.I LV
The
.B linear
type is equivalent to the
.B striped
type when one stripe exists.
In that case, the types can sometimes be used interchangably.
In most cases, the
.B mirror
type is deprecated and the
.B raid1
type should be used. They are both implementations of mirroring.
In some cases, an LV is a single device mapper (dm) layer above physical
devices. In other cases, hidden LVs (dm devices) are layered between the
visible LV and physical devices. LVs in the middle layers are called sub LVs.
A command run on a visible LV sometimes operates on a sub LV rather than
the specified LV. In other cases, a sub LV must be specified directly on
the command line.
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Striped raid types are
.B raid0/raid0_meta
,
.B raid5
(an alias for raid5_ls),
.B raid6
(an alias for raid6_zr) and
.B raid10
(an alias for raid10_near).
As opposed to mirroring, raid5 and raid6 stripe data and calculate parity
blocks. The parity blocks can be used for data block recovery in case devices
fail. A maximum number of one device in a raid5 LV may fail and two in case
of raid6. Striped raid types typically rotate the parity blocks for performance
reasons thus avoiding contention on a single device. Layouts of raid5 rotating
parity blocks can be one of left-asymmetric (raid5_la), left-symmetric (raid5_ls
with alias raid5), right-asymmetric (raid5_ra), right-symmetric (raid5_rs) and raid5_n,
which doesn't rotate parity blocks. Any \"_n\" layouts allow for conversion between
raid levels (raid5_n -> raid6 or raid5_n -> striped/raid0/raid0_meta).
raid6 layouts are zero-restart (raid6_zr with alias raid6), next-restart (raid6_nr),
next-continue (raid6_nc). Additionally, special raid6 layouts for raid level conversions
between raid5 and raid6 are raid6_ls_6, raid6_rs_6, raid6_la_6 and raid6_ra_6. Those
correspond to their raid5 counterparts (e.g. raid5_rs can be directly converted to raid6_rs_6
and vice-versa).
raid10 (an alias for raid10_near) is currently limited to one data copy and even number of
sub LVs. This is a mirror group layout thus a single sub LV may fail per mirror group
without data loss.
Striped raid types support converting the layout, their stripesize
and their number of stripes.
The striped raid types combined with raid1 allow for conversion from linear -> striped/raid0/raid0_meta
and vice-versa by e.g. linear <-> raid1 <-> raid5_n (then adding stripes) <-> striped/raid0/raid0_meta.
2017-02-11 01:20:19 +03:00
Sub LVs can be displayed with the command
.B lvs -a
