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SSDs for ZIL (Log)

cmdematos

Junior Member
Joined
Dec 24, 2014
Messages
12
I have 4x 256Gb SSDs setup as Log (mirrored). Maybe I should just have used two...

1) How can I remove just 2 from the mirrored set of 4 without starting the pool from scratch (lots of data and shares and configuration...)

2) How can I setup the zfs_nocacheflush option. I want to use the LOG for as much as possible and allow flushes to be async, none of this flush-every-5-seconds business...
PS: I think the freenas equivalent is possibly set Sync to Disabled for the pool?
 

Patrick M. Hausen

Dedicated Sage
Joined
Nov 25, 2013
Messages
1,671
You can remove slog vdevs from a pool. Just remove all of them via zpool offline, zpool detach and then re-add as you see fit.

HTH, Patrick
 

hervon

Senior Member
Joined
Apr 23, 2012
Messages
319
Documentation has it's purpose : https://www.ixsystems.com/documentation/freenas/11.3-RELEASE/storage.html

10.2.3. Adding Cache or Log Devices
Pools can be used either during or after pool creation to add an SSD as a cache or log device to improve performance of the pool under specific use cases. Before adding a cache or log device, refer to the ZFS Primer to determine if the system will benefit or suffer from the addition of the device.
To add a Cache or Log device during pool creation, click the Add Cache or Add Log button. Select the disk from Available Disks and use the right arrow next to Cache VDev or Log VDev to add it to that section.
To add a device to an existing pool, Extend that pool.

10.2.4. Removing Cache or Log Devices
Cache or log devices can be removed by going to Storage ➞ Pools. Choose the desired pool and click  (Settings) ➞ Status. Choose the log or cache device to remove, then click  (Options) ➞ Remove.
 

jgreco

Resident Grinch
Moderator
Joined
May 29, 2011
Messages
12,819
I have 4x 256Gb SSDs setup as Log (mirrored). Maybe I should just have used two...

1) How can I remove just 2 from the mirrored set of 4 without starting the pool from scratch (lots of data and shares and configuration...)

2) How can I setup the zfs_nocacheflush option. I want to use the LOG for as much as possible and allow flushes to be async, none of this flush-every-5-seconds business...
PS: I think the freenas equivalent is possibly set Sync to Disabled for the pool?
You sound a little confused.

There's no value that I can think of in putting more than two SSD's (mirrored) in as a SLOG device.

The log is NEVER used except upon pool import. It is not a write cache. ZFS flushes a transaction group to disk every five seconds. The SLOG has basically nothing to do with that.

https://www.ixsystems.com/community/threads/some-insights-into-slog-zil-with-zfs-on-freenas.13633/
 

cmdematos

Junior Member
Joined
Dec 24, 2014
Messages
12
Documentation has it's purpose : https://www.ixsystems.com/documentation/freenas/11.3-RELEASE/storage.html

10.2.3. Adding Cache or Log Devices
Pools can be used either during or after pool creation to add an SSD as a cache or log device to improve the performance of the pool under specific use cases. Before adding a cache or log device, refer to the ZFS Primer to determine if the system will benefit or suffer from the addition of the device.
To add a Cache or Log device during pool creation, click the Add Cache or Add Log button. Select the disk from Available Disks and use the right arrow next to Cache VDev or Log VDev to add it to that section.
To add a device to an existing pool, Extend that pool.

10.2.4. Removing Cache or Log Devices
Cache or log devices can be removed by going to Storage ➞ Pools. Choose the desired pool and click  (Settings) ➞ Status. Choose the log or cache device to remove, then click  (Options) ➞ Remove.

- Thank you. You made it simple, and documentation has its purpose, one wonders why the forums exists then, I think it represents a failure of documentation, or people, or both.

On 10.2.4 .. I had tried this, and I get an unsatisfactory "freenasUI.middleware.exceptions.MiddlewareError: [MiddlewareError: Disk could not be removed: "cannot remove /dev/gptid/6068dd06-2b74-11ea-95f8-00155d04020f: operation not supported on this type of pool, "] error message.

I think the first answer from Patrick may have the answer. I notice that his answer is succint and has no veneer of sneer to it at all, answered like a pro so even before trying it, I am confident it will work.

Thank you again.
 

hervon

Senior Member
Joined
Apr 23, 2012
Messages
319
Glad I could help. [ignore]
 
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