Dne 7.9.2017 v 10:06 lejeczek napsal(a):
hi fellas
I'm setting up a lvm raid0, 4 devices, I want raid0 and I understand & expect
- there will be four stripes, all I care of is speed.
I do:
$ lvcreate --type raid0 -i 4 -I 16 -n 0 -l 96%pv intel.raid0-0 /dev/sd{c..f} #
explicitly four stripes
I see:
$ mkfs.xfs /dev/mapper/intel.sataA-0 -f
meta-data=/dev/mapper/intel.sataA-0 isize=512 agcount=32, agsize=30447488 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0, sparse=0
data = bsize=4096 blocks=974319616, imaxpct=5
= sunit=4 swidth=131076 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal log bsize=4096 blocks=475744, version=2
= sectsz=512 sunit=4 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
What puzzles me is xfs's:
sunit=4 swidth=131076 blks
and I think - what the hexx?
Unfortunatelly 'swidth' in XFS has different meaning than lvm2's stripe
size parameter.
In lvm2 -
-i | --stripes - how many disks
-I | --stripesize - how much data before using next disk.
So -i 4 & -I 16 gives 64KB total stripe width
----
XFS meaning:
suinit = <RAID controllers stripe size in BYTES (or KiBytes when used with k)>
swidth = <# of data disks (don't count parity disks)>
----
---- so real-world example ----
# lvcreate --type striped -i4 -I16 -L1G -n r0 vg
or
# lvcreate --type raid0 -i4 -I16 -L1G -n r0 vg
# mkfs.xfs /dev/vg/r0 -f
meta-data=/dev/vg/r0 isize=512 agcount=8, agsize=32764 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=0, rmapbt=0,
reflink=0
data = bsize=4096 blocks=262112, imaxpct=25
= sunit=4 swidth=16 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal log bsize=4096 blocks=552, version=2
= sectsz=512 sunit=4 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
---- and we have ----
sunit=4 ... 4 * 4096 = 16KiB (matching lvm2 -I16 here)
swidth=16 blks ... 16 * 4096 = 64KiB
so we have 64 as total width / size of single strip (sunit) -> 4 disks
(matching lvm2 -i4 option here)
Yep complex, don't ask... ;)
In a LVM non-raid stripe scenario I've always remember it was: swidth = sunit
* Y where Y = number of stripes, right?
I'm hoping some expert could shed some light, help me(maybe others too)
understand what LVM is doing there? I'd appreciate.
many thanks, L.
We in the first place there is major discrepancy in the naming:
You use intel.raid0-0 VG name
and then you mkfs device: /dev/mapper/intel.sataA-0 ??
While you should be accessing: /dev/intel.raid0/0
Are you sure you are not trying to overwrite some unrelated device here?
(As your shown numbers looks unrelated, or you have buggy kernel or blkid....)
Regards
Zdenek
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