mirror of
git://sourceware.org/git/lvm2.git
synced 2024-12-21 13:34:40 +03:00
66 lines
2.7 KiB
Plaintext
66 lines
2.7 KiB
Plaintext
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.
|
|
|
|
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.
|
|
|
|
Sub LVs can be displayed with the command
|
|
.B lvs -a
|
|
|