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Slideshow explaining VDev, zpool, ZIL and L2ARC for noobs!

Ericloewe

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And hot spares can naturally be removed, for whatever reason.

The guide is slightly out of date, though. Starting with FreeNAS 11.2, you can remove vdevs from pools made up exclusively of single disks/mirrors.
 
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Starting with FreeNAS 11.2, you can remove vdevs from pools made up exclusively of single disks/mirrors.
11.2?... Is that a typo by any chance? Not that I'm seconding guessing you or anything but I thought it was further off than that.
 

danb35

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No, FreeNAS 11.2 is out in a beta release.
I know 11.2 is out in beta.

What I meant is that I thought the the ability to remove a vdev wasn't gonna see the light of day until 11.3 or later... perhaps I'm thinking of adding disks to RAIDz1.
 

danb35

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What I meant is that I thought the the ability to remove a vdev wasn't gonna see the light of day until 11.3 or later.
Nope, it's here now. I don't know that there's a milestone set for growing RAIDZ vdevs.
 

Chris Moore

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rmccullough

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rmccullough

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Perhaps he is trolling. I can't imagine anyone really having that much trouble understanding.

Great example.
I apologize, I didn't intend to troll. I was asking an earnest question. I tend to be careful when I use "absolute" terms unless I am "absolutely" sure.

In this instance, it was understanding what was meant by "it cannot be removed for any reason", I assumed it meant I could still remove it and break the pool, but there is a cliche about what "assume" does...

Same with "You cannot add more hard drives to a VDev once it is created." I think a less ambiguous statement would be "You cannot change the number of hard drives in a VDev once it is created."

Regardless, thank you for the clarifications gentlemen, I appreciate it.
 

Chris Moore

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I apologize, I didn't intend to troll.
I guess I am in a bad mood today because I really want to be snarky, but I am going to try to give you some useful information instead. If a number of drives are disconnected from the pool unexpectedly, the pool will often be able to recover when the drives are reconnected. A hardware RAID controller would usually not be able to recover from this but I have been in a situation where half the drives in the pool were disconnected when the drive controller failed. The pool went offline and the data was not accessible. Once we installed a replacement HBA (SAS controller) and booted the system back up, the pool was back online and all data was again available and consistent with the last known state prior to the fault. ZFS is very resilient and there are a lot of people here on the forum that will try to help you any way we can to get you started in the right direction.
 

rmccullough

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Thank you @Chris Moore. I appreciate your insights and perspective.
 

seanm

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This slideshow was very informative! Thanks Cyberjock!

This part caught my eye, since we are now 2019:

"RAIDZ1 provide redundancy from any single disk failure. However, due to disk sizes increasing faster than hard drive reliability, RAIDZ1 is really not safe. This is expected to continue for the foreseeable future. Eventually even RAIDZ2 will no longer be safe(estimated at around 2019)."

Is the 2019 prediction correct for RAIDZ2?
 

Chris Moore

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This is expected to continue for the foreseeable future. Eventually even RAIDZ2 will no longer be safe(estimated at around 2019)."

Is the 2019 prediction correct for RAIDZ2?
As drive sizes continue to increase, I expect it will eventually be a problem, but it depends on the tolerance of the user to potential faults and the expected reliability of the drives. There are some users on the forum that want RAIDz3 even now as a precaution against drive failure.
 
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Thank you for putting up this documentation!
It helped a lot.
 
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I just read the PDF and thought the same as seanm.
Just as I've bought hardware and planning to build my NAS with RAIDZ2 (6 x 4TB WD Red drives).
 
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Regarding the "You cannot add more hard drives to a VDev once it is created" line in the pdf:
  • if my pool consists of 2 drives in a mirror, that's a vdev, right? I can't add a third to achieve a 3-way mirror?
  • if my pool consists of 4 drives in a RAID-10 (2 mirrors striped, each mirror is a vdev, right?) I can't add a third drive to one of the mirrors?
 

danb35

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"You cannot add more hard drives to a VDev once it is created"
Mirrors are the exception. You can add a disk to a single-disk vdev to turn it into a two-disk mirror. You can add a disk to an n-way mirror to turn it into an n+1-way mirror. You can also remove disks from a mirror.
 

Chris Moore

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Although @danb35 is correct I think the changes to mirror vdevs would need to be done in the shell.
There's also work being done that would eventually also allow the expansion of a RAIDz2 vdev. Really, any RAIDz(x) level.
 

danb35

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I think the changes to mirror vdevs would need to be done in the shell.
Correct; despite multiple requests the devs haven't felt it was worth the "less than a day" of work to implement it properly in the GUI.
There's also work being done that would eventually also allow the expansion of a RAIDz2 vdev.
Yes, and very much anticipated it is too.
 

Chris Moore

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if my pool consists of 4 drives in a RAID-10
We just don't use that terminology. It would be described as a pool of mirrored vdevs; kind of like this pool in my server:

iSCSI pool: 8 vdevs with 2 x 1 TB drives each mirrored (16 Seagate Barracuda drives - ST1000DX001-1NS162)

We use different terminology on purpose to avoid confusion with hardware RAID.
 

Yorick

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Looks like all copies of this are now gone, @cyberjock
 
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