Centos 7 / xfs : is there a reserved space setting for xfs like there is in ext4?

chrism01 · 09-11-2019, 01:43 AM

Hi Guys,

in the ext4 fs we can reduce the reserved space from default 5% to eg 2% if we want to use the extra space.

I have a system with a new xfs disk mnt with default settings and no data on it.
It's 6TB raw, 5.5TB formatted, for now...

Can I reduce the reserved space (if xfs has such a thing), as 0.5TB seems like a lot of space, even allowing for formatting overhead.

michaelk · 09-12-2019, 09:21 AM

xfs does not have reserved space and I agree that 0.5TB is quite excessive for overhead. As a simple test I created a 1 and 2 GB file that I formatted as xfs. In either case the used space was the same, 33M as displayed by the df command.

What happens when you run the xfs_check and xfs_repair commands.

syg00 · 09-12-2019, 09:51 AM

Phttt - it's only 8 and a bit percent ....

If I had to guess, I saw it's "ducks and drakes". The vendor sold you a 6 TB drive, and XFS formatted a 5.5 TiB filesystem. Disk sizes are a scam - 1000 versus 1024 for a k is just the start ...

chrism01 · 09-13-2019, 01:15 AM

I guess syg00 is probably right.

Unfortunately, we've started using it (it's a backup system we needed stat), so I probably won't get a chance to run the cmds michaelk suggested, as they both require unmounting or at least making it read-only - not going to happen now...

Thanks anyway - I'll, maybe try them next time.

syg00 · 09-13-2019, 03:53 AM

Read this - there are other articles as well. The numbers start to get your attention as they get bigger.
Note also that the reserved space on ext? is in the filesystem, so would not show in this context anyway.

michaelk · 09-13-2019, 08:03 AM

syg00 is correct reserved space is part of the filesystem. From what I read and what I think are ~ real numbers is a bit different on my system so I will need to look into it a bit further. Yes it depends if 6TB is the manufactures disk size or the actual raw partition size and if the reference is decimal or binary.

The /boot partition on one of my systems is 1GB. Just for some quick numbers parted reports it as raw = 1074MB and formatted df -h = 1014MB which is about 5.6%