Swap Space and Drive Replacement

[Aaron C. de Bruyn]

My understanding is that FreeNAS creates swap space at the end of every drive we add to a pool.

For example, if I create a MIRROR out of 2x1 TB drives, it will shave a few gigs of space off the end of each drive.

So how does that work when you replace a drive?

I tested, and FreeBSD crashed with a bunch of pager errors when I pull a drive that I have offlined from the CLI.
I haven't tested from the GUI. Does FreeNAS do something special from the web interface to release that swap space?

 

[dlavigne]

Does FreeNAS do something special from the web interface to release that swap space?

Yes. From http://doc.freenas.org/9.3/freenas_storage.html#replacing-a-failed-drive:

If the disk is formatted with ZFS, click the disk’s entry then its “Offline” button in order to change that disk’s status to OFFLINE. This step is needed to properly remove the device from the ZFS pool and to prevent swap issues.

 

[Aaron C. de Bruyn]

Isn't this method rather unstable?
If FreeNAS is using swap space from individual drives, wouldn't a single drive failure cause that swap space to be unavailable? Seems to me this would lead to a crash.
If I have a system with 64 GB RAM, why would swap space be needed? Alternatively, why isn't the swap space on one of the pools instead of individual drives? Maybe use part of my SSD boot mirror?

 

[Ericloewe]

Swap is for emergencies only. It's not regularly used.

In any case, FreeNAS 10 will have more reliable swap.

 

[Bidule0hm]

Swap on a ZFS pool? that would be fun :)

 

[Ericloewe]

Swap on a ZFS pool? that would be fun :)

No, GEOM RAID1 of the swap partitions, for a RAID10 sort of scheme.
At least that's the plan, last I read.

 

[Aaron C. de Bruyn]

Swap on a ZFS pool? that would be fun :)

Yeah. I remembered a few minutes after I posted it that the system I was racking my brain for was 'GEOM'. Sorry, I grew up with Linux. All the fancy BSD subsystems are alien to me. ;)

 

[sfcredfox]

In line with OP, does anyone know why it's 'strongly discouraged' to disable the default swap space created when adding disks? If you provided a different location for SWAP, and

Swap is for emergencies only. It's not regularly used.

, then why discourage removing it.

While this issues was cause when the operator went against the system's documented procedure (must use GUI to remove drives safely), I have read some posts where people have complained of systems having problems when a disk goes down. Just curious, not really looking to challenge the system's design if this falls into the category of 'we just designed it like that, and doing it different breaks stuff'.

 

[Ericloewe]

In line with OP, does anyone know why it's 'strongly discouraged' to disable the default swap space created when adding disks? If you provided a different location for SWAP, and , then why discourage removing it.

While this issues was cause when the operator went against the system's documented procedure (must use GUI to remove drives safely), I have read some posts where people have complained of systems having problems when a disk goes down. Just curious, not really looking to challenge the system's design if this falls into the category of 'we just designed it like that, and doing it different breaks stuff'.

Swap is there to allow for slightly smaller drives to be resilvered in place of the slightly larger one.