[OpenIndiana-discuss] [illumos-Developer] ZFS spare disk usage issue

[Roy Sigurd Karlsbakk]

I understand that some of it may be a simple bug, but should it hang _all_ the pools? That's what happens when the third drive is removed... 

roy 

----- Original Message -----


This looks like a pretty simple bug. The issue is that the state of the SPARE vdev is being reported as REMOVED instead of DEGRADED. If it were the latter (as it should be), then everything would work just fine. Please file a bug at bugs.illumos.org . 


On a side note, this continues to expose the overly simplistic vdev state model used by ZFS (one which I can take a bulk of the responsibility for). Back before the days of ditto blocks and SPA3.0, it was sufficient to model state as a fairly binary proposition. But this now has ramifications that don't necessarily make sense. For example, one may be able open a pool even if a toplevel vdev is faulted. And even when a spare has finished resilvering, it's left in the DEGRADED state, which has implications for allocation policies (though I remember discussions around changing this). But the pool state is derived directly from the toplevel vdev state, so if you switch spares to be ONLINE, then 'zpool status' would think your pool is perfectly healthy. In this case it's true from a data protection standpoint, but not necessarily from a "all is well in the world" standpoint, as you are down one spare, and that spare may not have the same RAS properties as other devices in your RAID-Z stripe (it may put 3 disks on the same controller in one stripe, for example). 


- Eric 


On Fri, Mar 4, 2011 at 7:06 AM, Roy Sigurd Karlsbakk < roy at karlsbakk.net > wrote: 


Hi all 

I just did a small test on RAIDz2 to check whether my suspicion was right about ZFS not treating spares as replicas/copies of drives, and I think I've found it true. The short story: If two spares replaces two drives in raidz2, losing a third drive, even with the spares active, makes the pool unavailable. See full report on 

ODT: http://karlsbakk.net/ZFS/ZFS%20Spare%20disk%20usage.odt 
PDF: http://karlsbakk.net/ZFS/ZFS%20Spare%20disk%20usage.pdf 

Vennlige hilsener / Best regards 

roy 
-- 
Roy Sigurd Karlsbakk 
(+47) 97542685 
roy at karlsbakk.net 
http://blogg.karlsbakk.net/ 
-- 
I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og relevante synonymer på norsk. 

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Eric Schrock 
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-- 
Vennlige hilsener / Best regards 

roy 
-- 
Roy Sigurd Karlsbakk 
(+47) 97542685 
roy at karlsbakk.net 
http://blogg.karlsbakk.net/ 
-- 
I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og relevante synonymer på norsk.