Disk part of zpool for unknown reasons

[smiba]

Hi, first time posting here.

I was trying to test out ZIL/L2ARC on the two SSD's I have in my system where I was under the impression you can remove them at any time.

After I saw no performance improvement (Most likely due a misconfiguration, I'm not sure still new), I decided to remove them with the following command:

Code:

freenas# zpool status Main_Pool
  pool: Main_Pool
state: ONLINE
  scan: none requested
config:

  NAME  STATE  READ WRITE CKSUM
  Main_Pool  ONLINE  0  0  0
   raidz2-0  ONLINE  0  0  0
    gptid/1d7c862f-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/1e5bad68-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/1f32396f-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/1ff461ad-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/20c21c35-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/2180eedd-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/2252c655-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/230911f1-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
   gptid/ec227457-edd5-11e5-8ed7-00074305cc38  ONLINE  0  0  0
  logs
   gptid/f294fbab-edd5-11e5-8ed7-00074305cc38  ONLINE  0  0  0

errors: No known data errors
freenas# zpool remove Main_Pool gptid/f294fbab-edd5-11e5-8ed7-00074305cc38

This left me with one of the SSD's (gptid/ec227457-edd5-11e5-8ed7-00074305cc38) still in the pool, but its unremoveable.

Code:

freenas# zpool status Main_Pool
  pool: Main_Pool
state: ONLINE
  scan: none requested
config:

  NAME  STATE  READ WRITE CKSUM
  Main_Pool  ONLINE  0  0  0
   raidz2-0  ONLINE  0  0  0
    gptid/1d7c862f-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/1e5bad68-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/1f32396f-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/1ff461ad-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/20c21c35-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/2180eedd-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/2252c655-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
    gptid/230911f1-ed63-11e5-9a6f-00074305cc38  ONLINE  0  0  0
   gptid/ec227457-edd5-11e5-8ed7-00074305cc38  ONLINE  0  0  0

errors: No known data errors
freenas# zpool remove Main_Pool gptid/ec227457-edd5-11e5-8ed7-00074305cc38
cannot remove gptid/ec227457-edd5-11e5-8ed7-00074305cc38: only inactive hot spares, cache, top-level, or log devices can be removed

(I'm currently moving all my data over, and this is a screenshot of the stuck SSD. I've added it around 14:25)

What is its purpose right now? Because its being used, so its not idleing in there.

How do I remove it from the pool?

 

[joeschmuck]

Just a guess but I think your SSD is now part of your pool and if it dies, your entire pool is gone. Do not remove it, copy all your data off your system and then destroy your pool, remove the SSD and rebuild your pool.

Oh, what your drive is doing looks like it's being added to your pool and copying data to it.

 

[smiba]

Alright thanks, I was only at 1.3TB/9TB of the migration so I simply removed the pool and started the copy again.

Any tips on how to properly configure a part of the SSD's as cache?

 

[Robert Trevellyan]

Any tips on how to properly configure a part of the SSD's as cache?

http://doc.freenas.org/9.3/freenas_storage.html#extending-a-zfs-volume

Looks like you didn't choose Cache for volume layout when you added the SSD.

 

[joeschmuck]

Time to ask a question... What is your system hardware (RAM in particular) and why do you want to add a ZIL and SLOG?

 

[smiba]

CPU: i3-6100
RAM: 32GB DDR4-ECC (2 of the 4 slots used)
HDD: 8x WD RED 4TB
SDD: 2x Samsung 850 Pro 128GB
M1015 HBA in IT mode

I want to use it for making iSCSI storage faster and handle burst file transfer & the few files that often get loaded by my software better

I don't really care if it will only improve the speed a little bit since I already got the SSD's anyways. (And at worst I can always remove the cache drives from the array again, right?)

 

[joeschmuck]

32GB of RAM and an L2Arc will not help your performance in general and likely harm it. Add as much RAM as you can, you will benefit from that. Additionally your pol is not optimized for iSCSI, I believe you would be better off running multiple vdevs in a pool or mirrors to improve performance. There is a lot of particulars when using iSCSI and I'm not the expert.

Yes, if things are not going well you can remove the L2Arc, it's actually easy to do, however if you goof it up then you risk loosing your data.

 

[smiba]

I just added the two SSDs in stripe as L2ARC, I'll see if there are any improvements to the speed after a few days (so it can warm up). If there is none (or it even hurts performance like you said) I'll remove and sell them again

Thanks for your help by the way

 

[joeschmuck]

FYI, the only way these will help you is if you are requesting the same information very frequently. For example, if you have a spreadsheet or database which many people access, that could make things a bit speedier but if you stream videos or are requesting a lot of different data and rarely using the same data, the performance tanks because the system will first look at the Arc (RAM) and not find it, L2Arc for the data and it's not there either, it will then go fetch it from the drives. It may sound negligible but you added a bottleneck, or should I say that most people add this bottleneck thinking an L2Arc would help them when it does not.

Well good luck on that system.