On 8/29/17 11:18 PM, Donald Douwsma wrote:
> 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>
Interesting. Yeah, I suppose this makes sense, though I'm surprised
anyone would notice. :)
Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx>
Thanks,
-Eric
> ---
> 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
>
--
To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
