zfs discuss - Jan 2011 - L2ARC - shared or associated with a pool?

Hi all

There was some discussion on #opensolaris recently about L2ARC being dedicated
to a pool, or shared. I figured since it''s associated with a pool, it
must be local, but I really don''t know.

So - is it local to a pool, or global?
If it''s global, will I need to do something for mypool''s l2arc
to be used for other pools?

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 element?rt imperativ for alle pedagoger ? unng? eksessiv anvendelse av
idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og
relevante synonymer p? norsk.

Roy,
> Hi all
> 
> There was some discussion on #opensolaris recently about L2ARC being
dedicated to a pool, or shared. I figured since it''s associated with a
pool, it must be local, but I really don''t know.
An L2ARC is made up of one or more "Cache Devices" associated with a
single ZFS storage pool. Caching device(s) can be associated with a ZFS storage
pool at either ''zpool create ...'' time or later with
''zpool add ...''

	# zpool create pool_0 mirror c8t0d0 c9t0d0 mirror c8t0d1 c9t0d1 cache c7t0d0
c7t1d0
or
	# zpool add pool_0 cache c7t0d0 c7t1d0

If one finds that a caching device is being underutilized within a given ZFS
storage pool it can be removed, and reprovisioned into another pool.

	# zpool remove pool_0 cache c7t1d0
	# zpool add pool_1 cache c7t1d0

In regards to sharing of cache devices between multiple ZFS storage pools, ZFS
supports taking a device, using ''format ....'' to partition the
device into multiple slices, and then to add selected slices into different ZFS
storage pools. For data devices in a ZFS storage pool this disables the
Write-Cache-Enable setting, potentially impacting performance, but this does not
appear to impact SSD devices, when used as either log or cache devices.

	# zpool remove pool_0 cache c7t1d0
	# format c7t1d0
	format > ....
		.
		.
	# zpool add pool_0 cache c7t1d0s0
	# zpool add pool_1 cache c7t1d0s1 (or other slices based on the manual
formatting done above)

NOTE: The omission of either slice designator (''s0'' or
''s1'' above), will cause ZFS to (re)format the whole device,
undoing any manual partitioning done with format.

Jim
> 
> So - is it local to a pool, or global?
> If it''s global, will I need to do something for mypool''s
l2arc to be used for other pools?
> 
> 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 element?rt imperativ for alle pedagoger ? unng? eksessiv anvendelse av
idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og
relevante synonymer p? norsk.
> _______________________________________________
> zfs-discuss mailing list
> zfs-discuss at opensolaris.org
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