[This is silly and has no real purpose except to explore the limits.
If that offends you, don't read the rest of this email.]
I am trying to create an XFS filesystem in a partition of approx
2^63 - 1 bytes to see what happens.
This creates a 2^63 - 1 byte virtual disk and partitions it:
# nbdkit memory size=9223372036854775807
# modprobe nbd
# nbd-client localhost /dev/nbd0
# blockdev --getsize64 /dev/nbd0
9223372036854774784
# gdisk /dev/nbd0
[...]
Command (? for help): n
Partition number (1-128, default 1):
First sector (18-9007199254740973, default = 1024) or {+-}size{KMGTP}:
Last sector (1024-9007199254740973, default = 9007199254740973) or {+-}size{KMGT
P}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300):
Changed type of partition to 'Linux filesystem'
Command (? for help): w
The first problem was that the standard mkfs.xfs command will
try to trim the disk in 4 GB chunks (I believe this is a limit
imposed by the kernel APIs). For a 8 EB image that takes forever.
However I can use the -K option to get around that:
# mkfs.xfs -K /dev/nbd0p1
meta-data=/dev/nbd0p1 isize=512 agcount=8388609, agsize=268435455 blks
= sectsz=1024 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=0, rmapbt=0, reflink=0
data = bsize=4096 blocks=2251799813684987, imaxpct=1
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal log bsize=4096 blocks=521728, version=2
= sectsz=1024 sunit=1 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
mkfs.xfs: read failed: Invalid argument
I guess this indicates a real bug in mkfs.xfs. I've not tracked down
exactly why this syscall fails yet but will see if I can find it
later.
But first I wanted to ask a broader question about whether there are
other mkfs options (apart from -K) which are suitable when creating
especially large XFS filesystems?
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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