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Richard T
Asked: 2020-08-15 19:56:13 +0800 CST

On modern Linux, is it safe, or is it a bad idea to move all active writes of the OS to other disks?

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I've been using SSDs long enough now to think about protecting them from premature failure due to excessive writes. So, I've already moved /var to other disks successfully (be they other SSDs or HDDs) and it works fine, but I'm a little hesitant to move /run or any other write areas. Perhaps my fears are unfounded.

I am not necessarily familiar with ALL the write areas of the system disk. Of course the most used is /var, and it's my perception that /run is next, but this question is actually asking about ALL of them. If you know of something other than /var and /run that are written to, well, first I'd like to know about them and secondly I'd like to know if they can be safely moved or not.

I just don't know enough about the boot environment in modern Linux (I'm presently mostly on Fedora Server 32). If the disk that these alternative write locations are on aren't already mounted when needed, then this obviously can't work. In looking through the system logs, it's not easy to tell when said transition happens.

Comments received seem to not fully appreciate the main point:

Is it not true that an SSD with only reads will live a lot longer?

If true, which seems to be a foregone conclusion is true from the very definition that they're write-limited, then, isn't it a valuable exercise to move as much write activity off a system disk as reasonable to preserve its life?

I think some people just don't care about that. I'd guess that said people are well financed and can easily afford the man hours and whatever else. But in these trying times, especially during this pandemic when smaller organizations are stressed to their limits, this question is very pertinent. ... It's not the cost of the drive as much as it is the labor to replace it. People who do not fund such things themselves may not appreciate the challenge presented.

ssd fedora-32

1 Answers

  1. Best Answer

    To sort-of answer the original question, we make embedded systems where we are interested in minimizing writes. The OS partitions are writeable flash, but we mount them read-only, and offload the following:

    /etc/{adjtime|resolv.conf}
/etc/lvm/{cache|archive|backup}
/var/{gdm|log|cache|account|spool}
/var/db/nscd
/var/systemd/timers
/var/empty/sshd/etc/localtime
/var/lib/systemd/random-seed
/var/lib/{xkb|puppet|dbus|postfix|dav|dhcpd|dhclient|php|pulse|ups|arpwatch|NetworkManager|gdm|iscsi|logrotate.status|ntp|xen|samba|nfs}

    This is for a RHEL-derived system and in our case we put the writeable areas in RAM (data loss is not an issue for us). Granted we are not using SSDs and this is not your exact question, however it should go a long way toward indicating what you should look to offload if you wish to reduce/eliminate writes. You may need more/less than these depending on your packages and config.

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