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man: lvcreate correction on --stripes explanation and examples

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with respect to the changed, configurable default behaviour
     introduced with commit 7eb7909193.

     E.g. raid default of 2 stripes rather than number of PVs in the VG
     or on the command line minus one.
This commit is contained in:
Heinz Mauelshagen 2016-07-28 17:34:42 +02:00
parent 02ddd48c11
commit 8d959b6c75
1 changed files with 21 additions and 8 deletions
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29
man/lvcreate.8.in
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@ -603,14 +603,24 @@ for online conversion to thin volumes with external origin.
.br .br
Gives the number of stripes. Gives the number of stripes.
This is equal to the number of physical volumes to scatter This is equal to the number of physical volumes to scatter
the logical volume. When creating a RAID 4/5/6 logical volume, the logical volume data. When creating a RAID 4/5/6 logical volume,
the extra devices which are necessary for parity are the extra devices which are necessary for parity are
internally accounted for. Specifying \fB\-i 3\fP internally accounted for. Specifying \fB\-i 3\fP
would use 3 devices for striped logical volumes, would cause 3 devices for striped and RAID 0 logical volumes,
4 devices for RAID 4/5, and 5 devices for RAID 6. Alternatively, 4 devices for RAID 4/5, 5 devices for RAID 6 and 6 devices for RAID 10.
RAID 4/5/6 will stripe across all PVs in the volume group or Alternatively, RAID 0 will stripe across 2 devices,
all of the PVs specified if the \fB\-i\fP RAID 4/5 across 3 PVs, RAID 6 across 5 PVs and RAID 10 across
argument is omitted. 4 PVs in the volume group if the \fB\-i\fP argument is omitted.
In order to stripe across all PVs of the VG if the \fB\-i\fP argument is
omitted, set raid_stripe_all_devices=1 in the allocation
section of \fBlvm.conf (5)\fP or add
.br
\fB\-\-config allocation/raid_stripe_all_devices=1\fP
.br
to the command.
.br
Note the current limitation of 8 stripes total in any RaidLV including parity devices.
Two implementations of basic striping are available in the kernel. Two implementations of basic striping are available in the kernel.
The original device-mapper implementation is the default and should The original device-mapper implementation is the default and should
normally be used. The alternative implementation using MD, available normally be used. The alternative implementation using MD, available
@ -801,9 +811,12 @@ a parity drive for a total of 4 devices) and a stripesize of 64KiB:
.B lvcreate \-\-type raid5 \-L 5G \-i 3 \-I 64 \-n my_lv vg00 .B lvcreate \-\-type raid5 \-L 5G \-i 3 \-I 64 \-n my_lv vg00
Creates a RAID5 logical volume "vg00/my_lv", using all of the free Creates a RAID5 logical volume "vg00/my_lv", using all of the free
space in the VG and spanning all the PVs in the VG: space in the VG and spanning all the PVs in the VG (note that the command
will fail if there's more than 8 PVs in the VG in which case \fB\-i 7\fP
has to be used to get to the currently possible maximum of
8 devices including parity for RaidLVs):
.sp .sp
.B lvcreate \-\-type raid5 \-l 100%FREE \-n my_lv vg00 .B lvcreate \-\-config allocation/raid_stripe_all_devices=1 \-\-type raid5 \-l 100%FREE \-n my_lv vg00
Creates a 5GiB RAID10 logical volume "vg00/my_lv", with 2 stripes on Creates a 5GiB RAID10 logical volume "vg00/my_lv", with 2 stripes on
2 2-way mirrors. Note that the \fB-i\fP and \fB-m\fP arguments behave 2 2-way mirrors. Note that the \fB-i\fP and \fB-m\fP arguments behave