Multiple mounts under a mount on a linux server

Question

I have a server that I mount some storage (LUNs) under. The first mount is

LUN0(20Gb) as /database

then under that I mount

LUN1(10Gb) as /database/logs

so in essence I can't mount /database/logs until /database is up and mounted.

Is this really bad? Is there a better way to do it? I think is its bad, but I have a DB Admin telling me its fine and that's the way he has done it before?

Answer 1

So, you're asking whether it is bad to mount another partition under a folder where a different partition is already mounted?

No, there's nothing wrong with that. Sometimes you even need or might want to do so, depending on what exactly is on the partitions. If you keep the database in LUN0 and are using LUN1 as a partition for it's logs, then you probably want to separate the logs from the actual database. In that case it is perfectly alright.

Answer 2

There are a couple of things that can happen if at some point the logs LUN is mounted before the database LUN is mounted.

Most likely the logs LUN will fail to mount because it's mount point does not exist.

If the mount point does exist mounting the database LUN later will make the logs LUN "invisible" because all files "below" a mount point are unavailable while a file system is mounted on it.

In both cases the logs will be written to the database LUN in the /database/logs directory which will obviously require downtime to clean up.