A no longer existing OST has been permanently disabled on the MGS using

lctl conf_param vegas-OST0059.osc.active=0

After this, clients hang on df (after lustre is remounted the next time). strace shows it hanging on a statfs call.

Tried with the lustre mount option lazystatfs (undocumented?) which is supposed to work around this issue, but it did not help with lustre 2.4.1, clients still hang on df. This is the standard df, lfs df seems to work OK.