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man lvcreate/lvconvert: minor clean up rewording

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David Teigland 2017-04-10 16:29:40 -05:00
parent a4f07b701a
commit 21da004e58
2 changed files with 51 additions and 45 deletions
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81
man/lvconvert.8_des
View File

@ -7,6 +7,17 @@ To display the current LV type, run the command:
.B lvs -o name,segtype
.I LV
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.
Sub LVs can be displayed with the command:
.B lvs -a
The
.B linear
type is equivalent to the
@ -20,45 +31,41 @@ 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).
\fBraid0/raid0_meta\fP,
\fBraid5\fP (an alias for raid5_ls),
\fBraid6\fP (an alias for raid6_zr) and
\fBraid10\fP (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.
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 and
data blocks for performance reasons, thus avoiding contention on a single
device. Specific arrangements of parity and data blocks (layouts) can be
used to optimize I/O performance, or to convert between raid levels. See
\fBlvmraid\fP(7) for more information.
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.
Layouts of raid5 rotating parity blocks can be: 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. Layouts of raid6 are: zero-restart (raid6_zr with alias
raid6), next-restart (raid6_nr), and next-continue (raid6_nc).
Sub LVs can be displayed with the command
.B lvs -a
Layouts including _n allow for conversion between raid levels (raid5_n to
raid6 or raid5_n to striped/raid0/raid0_meta). 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.

15
man/lvcreate.8_des
View File

@ -1,8 +1,8 @@
lvcreate creates a new LV in a VG. For standard LVs, this requires
allocating logical extents from the VG's free physical extents. If there
is not enough free space, then the VG can be extended (see
\fBvgextend\fP(8)) with other PVs, or existing LVs can be reduced or
removed (see \fBlvremove\fP, \fBlvreduce\fP.)
is not enough free space, the VG can be extended with other PVs
(\fBvgextend\fP(8)), or existing LVs can be reduced or removed
(\fBlvremove\fP(8), \fBlvreduce\fP(8).)
To control which PVs a new LV will use, specify one or more PVs as
position args at the end of the command line. lvcreate will allocate
@ -19,7 +19,7 @@ unique PVs be available in the VG for allocation.
Thin pools (for thin provisioning) and cache pools (for caching) are
represented by special LVs with types thin-pool and cache-pool (see
\fBlvmthin\fP(7) and \fBlvmcache\fP(7)). The pool LVs are not usable as
standard block devices, but the LV names act references to the pools.
standard block devices, but the LV names act as references to the pools.
Thin LVs are thinly provisioned from a thin pool, and are created with a
virtual size rather than a physical size. A cache LV is the combination of
@ -27,10 +27,9 @@ a standard LV with a cache pool, used to cache active portions of the LV
to improve performance.
.SS Usage notes
In the usage section below, \fB--size\fP \fISize\fP can be replaced
with \fB--extents\fP \fINumber\fP. See both descriptions
the options section.
with \fB--extents\fP \fINumber\fP. See descriptions in the options section.
In the usage section below, \fB--name\fP is omitted from the required
options, even though it is typically used. When the name is not
options, even though it is typically used. When the name is not
specified, a new LV name is generated with the "lvol" prefix and a unique
numeric suffix. Also see the description in the options section.
numeric suffix.