How to let certain HDDs sleep but keep Entware/Swap drive awake

[Klonoa]

Hi all,
I’m running an RT-AC86U with ASUSWRT and have a couple of USB HDDs connected. What I’d like to do is:

1. Let most of the drives spin down / go to sleep when idle.
2. Keep one specific drive always active, because it hosts Entware and also a Swap file.

The problem:

1. ASUSWRT’s built-in USB settings only apply globally, so I can’t exclude that one drive.
2. After a reboot the system changes the sdX device assignment, so I can’t just hard-code the drive either.

So basically I need a way to:

1. Automatically allow only some drives to sleep while excluding the Entware/Swap drive.
2. Maybe via a startup script or some smarter method that can identify the right disk even if sdX changes.

Has anyone here set this up successfully? Any tips would be appreciated

Thanks!

 

[FTC]

Hi, one method I have used to 'fix' the mount point name of the inserted drives is to give the partitions a label (with tune2fs). This way the drive is always mounted under /dev/mnt/labelname instead of /dev/mnt/sdbx
.
About how to sleep selectively some drives, I have not looked at this. In my environment I am using a thumbdrive as the device for swapping and other 'always live' stuff, thus avoiding the need to keep it alive explicitly (flash media does not support sleep anyways).

 

[Crimliar]

I think the majority of the regulars here use SSDs, and only one of them, keeping any serious storage on another device (NAS, server, etc). When doing that, SSDs may have "low power" states, but the energy savings from using them are usually negligible as to not be worth exploring!
*Using Merlin, my SSD has a swap file on it for the router. A couple of cameras also duplicate their storage via FTP to a directory, and I've a share set up so I can move files to the router if I need to (and it's the easiest way to access my security footage).