[linux-lvm] lv raid - how to read this?

[lejeczek]

On 07/09/17 10:16, Zdenek Kabelac wrote:
> 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....)
>

hi,
I renamed VG in the meantime,
I get xfs intricacy..
so.. question still stands..
why xfs format does not do what I remember always did in the 
past(on lvm non-raid but stripped), like in your example

          =                       sunit=4      swidth=16 blks
but I see instead:

          =                       sunit=4      
swidth=4294786316 blks

a whole lot:

$ xfs_info /__.aLocalStorages/0
meta-data=/dev/mapper/intel.raid0--0-0 isize=512    
agcount=32, agsize=30768000 blks
          =                       sectsz=512   attr=2, 
projid32bit=1
          =                       crc=1        finobt=0 
spinodes=0
data     =                       bsize=4096   
blocks=984576000, imaxpct=5
          =                       sunit=4      
swidth=4294786316 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal               bsize=4096   blocks=480752, 
version=2
          =                       sectsz=512   sunit=4 blks, 
lazy-count=1
realtime =none                   extsz=4096   blocks=0, 
rtextents=0

$ lvs -a -o +segtype,stripe_size,stripes,devices intel.raid0-0
   LV           VG            Attr       LSize   Pool Origin 
Data% Meta%  Move Log Cpy%Sync Convert Type   Stripe #Str 
Devices
   0            intel.raid0-0 rwi-aor--- 
3.67t                                                     
raid0 16.00k    4 
0_rimage_0(0),0_rimage_1(0),0_rimage_2(0),0_rimage_3(0)
   [0_rimage_0] intel.raid0-0 iwi-aor--- 938.96g linear     
0     1 /dev/sdc(0)
   [0_rimage_1] intel.raid0-0 iwi-aor--- 938.96g linear     
0     1 /dev/sdd(0)
   [0_rimage_2] intel.raid0-0 iwi-aor--- 938.96g linear     
0     1 /dev/sde(0)
   [0_rimage_3] intel.raid0-0 iwi-aor--- 938.96g linear     
0     1 /dev/sdf(0)


>
> Regards
>
> Zdenek