When sunit and swidth are used mkfs.xfs tries to avoid all allocation
groups aligning on the same stripe and will attempt to stagger them
across the stripes that make up swidth. If there is only one stripe
then there is no benefit in this optimisation.
$ truncate -s10G xfs_10G_su256k_sw1.image
$ mkfs.xfs -d su=256k,sw=1 xfs_10G_su256k_sw1.image
meta-data=xfs_10G_su256k_sw1.image isize=512 agcount=16, agsize=163776 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0, sparse=0
data = bsize=4096 blocks=2620416, imaxpct=25
= sunit=64 swidth=64 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal log bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=64 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
A side effect of the optimisation is that the size adjustment used to stager
the allocation groups causes the last sunit of storage to be unused.
$ echo $((2620416*4096))
10733223936
$ ls -l xfs_10G_su256k_sw1.image
-rw-rw-r--. 1 test test 10737418240 Aug 30 10:54 xfs_10G_su256k_sw1.image
Skip this optimisation when sunit == swidth.
Signed-off-by: Donald Douwsma <ddouwsma@xxxxxxxxxx>
---
mkfs/xfs_mkfs.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index b5c3a57..35dae48 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -2534,7 +2534,9 @@ reported by the device (%u).\n"),
}
}
}
- if (dswidth && ((agsize % dswidth) == 0) && (agcount > 1)) {
+ if (dswidth && ((agsize % dswidth) == 0)
+ && (dswidth != dsunit)
+ && (agcount > 1)) {
/* This is a non-optimal configuration because all AGs
* start on the same disk in the stripe. Changing
* the AG size by one sunit will guarantee that this
--
1.8.3.1
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