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The migration is almost done, at least the rest should happen in the background. There are still a few technical difference between the old cluster and the new ones, and they are summarized in this issue. Please pay attention to the TL:DR at the end of the comment.
The "which" utility is not guaranteed to be installed, and if it is, its behavior is not portable.
Conversely, the "command -v" shell builtin is required to exist in all POSIX 2008 compliant shells, and is thus guaranteed to work everywhere.
Examples of open-source shells likely to be installed as /bin/sh on Linux, which implement the 12-year-old standard: ash, bash, busybox, dash, ksh, mksh and zsh.
A side benefit of using the POSIX portable option is that it does not require an external disk executable to be forked. This therefore represents a mild speedup.