TrueNAS SCALE will create but not use 2GB SWAP on Pool Disks, only 2GB on Bootdisk

[dln_]

Hello all!

I'm in the process of evaluating several different NAS operating systems and I'm currently giving TrueNAS SCALE a go.

Show : Hardware Details

HP ProLiant Microserver Gen8
Intel Xeon E3-1265Lv2 8-core
16GB ECC Memory

Boot device: 64GB MicroSD Card in the Servers MicroSD slot
Disk for testing: 500GB WD Blue 3.5"

I am aware that using a MicroSD as boot medium is discouraged, but I accept the possible performance impact and looked out to pick a slightly more expensive card geared towards 24/7 use. The SD Card is connected trough a USB 2.0 bridge.

While installing TrueNAS SCALE I was given the option to put a 16GB SWAP partition onto my boot device.

I decided to add the Partition and now my partition configuration looks like this:

Code:

NAME     TYPE    SIZE MOUNTPOINT PARTTYPENAME             VENDOR   MODEL                  TRAN
sda      disk  465.8G                                     ATA      WDC_WD5000AAKX-07U6AA0 sata
├─sda1   part      2G            Linux swap
└─sda2   part  463.8G            Solaris /usr & Apple ZFS
sdb      disk   59.6G                                     HP iLO   Internal_SD-CARD       usb
├─sdb1   part      1M            BIOS boot
├─sdb2   part    512M            EFI System
├─sdb3   part   43.1G            Solaris /usr & Apple ZFS
└─sdb4   part     16G            Linux swap
  └─sdb4 crypt    16G [SWAP]

Notice the 2GB Linux swap partition on sda1. This partition does not appear to be in use by the system. Only the 16GB on the boot device (behind a dm-crypt mapper, is swap encrypted for security?)

Code:

NAME      TYPE      SIZE USED PRIO
/dev/dm-0 partition  16G   0B   -2

Nor does it even contain a valid swap signature.

Code:

swapon: /dev/sda1: read swap header failed

If I do not choose to create a 16GB SWAP on the bootdevice the 2GB SWAP partition on the pool disks is also created but still not used (swapon not outputting anything)

Code:

NAME   TYPE   SIZE MOUNTPOINT PARTTYPENAME             VENDOR  MODEL      TRAN
sda    disk  59.6G                                     HP iLO  Internal_S usb
|-sda1 part     1M            BIOS boot
|-sda2 part   512M            EFI System
`-sda3 part  59.1G            Solaris /usr & Apple ZFS
sdb    disk 465.8G                                     ATA     WDC_WD5000 sata
|-sdb1 part     2G            Linux swap
`-sdb2 part 463.8G            Solaris /usr & Apple ZFS

What's the reason to create an empty SWAP partition on disk like this? Should I do anything about it (run mkswap and add it with swapon)?

Cheers

 

[dln_]

Apologies, I made a mistake in the above post. Before posting the second lsblk output after reinstalling with no 16GB SWAP on the boot device, I did not recreate a storage pool on the 500GB. I did that now and sure enough, the 2GB do get used as swap space.

Code:

NAME     TYPE    SIZE MOUNTPOINT PARTTYPENAME             VENDOR  MODEL   TRAN
sda      disk   59.6G                                     HP iLO  Interna usb
|-sda1   part      1M            BIOS boot
|-sda2   part    512M            EFI System
`-sda3   part   59.1G            Solaris /usr & Apple ZFS
sdb      disk  465.8G                                     ATA     WDC_WD5 sata
|-sdb1   part      2G            Linux swap
| `-sdb1 crypt     2G [SWAP]
`-sdb2   part  463.8G            Solaris /usr & Apple ZFS

Code:

NAME      TYPE      SIZE USED PRIO
/dev/dm-0 partition   2G   0B   -2

Still, why does a 2GB swap partition get created and remains unused when there is also a 16GB on the boot disk?

 

[Samuel Tai]

This is carry-over from CORE, which creates 2GB FreeBSD-swap partitions, and is in place if you ever decide to move your pool disks back to CORE.

 

[danb35]

Still, why does a 2GB swap partition get created and remains unused

It is, as Samuel says, a carry-over from CORE. It's also there in case of minor variations in disk size, particularly in the case of disk replacement. If you bought a different model of disk with a slightly different (especially smaller) capacity, reducing the size of the swap partition--or removing it entirely--would still let you replace a failed disk.

 

[dln_]

This is carry-over from CORE, which creates 2GB FreeBSD-swap partitions, and is in place if you ever decide to move your pool disks back to CORE.

I see, so you could say its for backwards-compatibility.

Would it make sense to make use of it under the Debian Linux based SCALE if you already have 16GB on a boot device?

 

[Samuel Tai]

Would it make sense to make use of it under the Debian Linux based SCALE if you already have 16GB on a boot device?

It's your system. Can't hurt to use it. You may not get much benefit from it, or as a colleague of mine once put it: "The juice ain't worth the squeeze."