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Date:      Sat, 5 Nov 2022 11:59:13 -0700
From:      David Christensen <dpchrist@holgerdanske.com>
To:        questions@freebsd.org
Subject:   Re: Setting up ZFS L2ARC on a zvol
Message-ID:  <7a8ff099-dcae-c361-caab-98e9c44b8aa7@holgerdanske.com>
In-Reply-To: <20221105183934.9292e9232983713de5e1e3f8@sohara.org>
References:  <PH0PR20MB370438AB8180CE27187E3BD2C0309@PH0PR20MB3704.namprd20.prod.outlook.com> <c5c4a09f-c2f4-a76f-dd1d-e34b4fd8a63f@holgerdanske.com> <20221105183934.9292e9232983713de5e1e3f8@sohara.org>

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On 11/5/22 11:39, Steve O'Hara-Smith wrote:
> On Sat, 5 Nov 2022 10:39:53 -0700
> David Christensen <dpchrist@holgerdanske.com> wrote:
> 
>> ZPOOLCONCEPTS(7) for both 12.3-R [1] and 13.1-R [2]:
>>
>> "Virtual devices cannot be nested, so a mirror or raidz virtual device
>> can only contain files	or disks.  Mirrors of mirrors (or other
>> combinations) are not allowed.
> 
> 	Of course you can cheat to some extent using iscsi - I've used an
> iscsi mounted zvol as a zfs mirror for an SSD in a laptop.


Interesting.


I wonder if that trick would solve the OP's desire to create a ZFS 
volume on the NVMe pool and use it as a cache for the HDD pool?
And, if so, how to measure the additional CPU cycle and memory costs?



David




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