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Old 11-05-2009, 09:55 AM   #1
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Registered: Aug 2009
Location: Prague
Distribution: Kubuntu 8.10
Posts: 11

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Changing XFS sunit and swidth parameters on RAID 5

Hi all,

I would like to ask something regarding XFS and RAID 5:

I've built raid 5 from 4 1TB devices using 256KB chunk size.
I wanted to tweak XFS on it a little so I formatted it with

mkfs.xfs -f -L DATA -l internal,size=128m -d agcount=30,su=256k,sw=3 /dev/md0
Problem is that output shows:
eta-data=/dev/md0               isize=256    agcount=30, agsize=24419072 blks
         =                       sectsz=4096  attr=2
data     =                       bsize=4096   blocks=732571776, imaxpct=5
         =                       sunit=64     swidth=192 blks
naming   =version 2              bsize=4096   ascii-ci=0
log      =internal log           bsize=4096   blocks=32768, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=0
realtime =none                   extsz=786432 blocks=0, rtextents=0
That's not exactly sunit that I wanted (should be 512 and swidth 1536).
Even if I try to mount it with these options set to proper numbers, xfs_info still provides same output.

Any ideas or suggestions why this happens?


Old 11-10-2009, 03:01 PM   #2
LQ Newbie
Registered: Aug 2009
Location: Prague
Distribution: Kubuntu 8.10
Posts: 11

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In reference to

where it is stated that:
data = bsize=4096 blocks=84286944,
= sunit=16 swidth=48 blks,

since it apparently displays the "sunit" and "swidth" values in terms of
XFS blocks, which are 4096 bytes each....
That means that my 64*4096 is my 256k and swidth 192*4096/512 is my 1536.

Anyway, formatting without parameters resulted in the same numbers because xfs' built-in optimization for software raids.


raid5, xfs

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