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Add "devices/default_data_alignment" to lvm.conf to control the internal
default that LVM2 uses: 0==64k, 1==1MB, 2==2MB, etc.
If --dataalignment (or lvm.conf's "devices/data_alignment") is specified
then it is always used to align the start of the data area. This means
the md_chunk_alignment and data_alignment_detection are disabled if set.
(Same now applies to pvcreate --dataalignmentoffset, the specified value
will be used instead of the result from data_alignment_offset_detection)
set_pe_align() still looks to use the determined default alignment
(based on lvm.conf's default_data_alignment) if the default is a
multiple of the MD or topology detected values.
The new standard in the storage industry is to default alignment of data
areas to 1MB. fdisk, parted, and mdadm have all been updated to this
default.
Update LVM to align the PV's data area start (pe_start) to 1MB. This
provides a more useful default than the previous default of 64K (which
generally ended up being a 192K pe_start once the first metadata area
was created).
Before this patch:
# pvs -o name,vg_mda_size,pe_start
PV VMdaSize 1st PE
/dev/sdd 188.00k 192.00k
After this patch:
# pvs -o name,vg_mda_size,pe_start
PV VMdaSize 1st PE
/dev/sdd 1020.00k 1.00m
The heuristic for setting the default alignment for LVM data areas is:
- If the default value (1MB) is a multiple of the detected alignment
then just use the default.
- Otherwise, use the detected value.
In practice this means we'll almost always use 1MB -- that is unless:
- the alignment was explicitly specified with --dataalignment
- or MD's full stripe width, or the {minimum,optimal}_io_size exceeds
1MB
- or the specified/detected value is not a power-of-2
Introduce --norestorefile to allow user to override the new requirement.
This can also be overridden with "devices/require_restorefile_with_uuid"
in lvm.conf -- however the default is 1.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Update example.conf to describe vgmetadatacopies. Provide an
explanation for the '0' ("unmanaged") value.
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
