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Date:      Thu, 24 Nov 2011 14:29:41 -0500
From:      APseudoUtopia <apseudoutopia@gmail.com>
To:        Matthew Seaman <m.seaman@infracaninophile.co.uk>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Setting up ZFS - Filesystem Properties and Installing on Root
Message-ID:  <CAKOHg=PxYFJC2uOD04+axHUziaxXofU-qfyvS_Xm-NqNnWtCSw@mail.gmail.com>
In-Reply-To: <4ECE9A7F.9000107@infracaninophile.co.uk>
References:  <CAKOHg=PEqeMPN_2dfQ+4msi1j7CMUu=iO+pSuezRoa_CELzQtw@mail.gmail.com> <88f3d8e819b3420f8e61723bee90ba5e.squirrel@www.magehandbook.com> <CAKOHg=N4yt0vdac8aZMUTK+8EnoSwxhK+yWmy7MsOXvKrWEmyw@mail.gmail.com> <4ECB580E.20203@infracaninophile.co.uk> <CAKOHg=PWcpqHdyvaS+oRwghA5m-A-rMxF-wqw3ZAPERzmO+pRw@mail.gmail.com> <4ECE9A7F.9000107@infracaninophile.co.uk>

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On Thu, Nov 24, 2011 at 2:26 PM, Matthew Seaman
<m.seaman@infracaninophile.co.uk> wrote:
> On 24/11/2011 19:19, APseudoUtopia wrote:
>> On Tue, Nov 22, 2011 at 3:06 AM, Matthew Seaman
>> <m.seaman@infracaninophile.co.uk> wrote:
>>> On 22/11/2011 02:09, APseudoUtopia wrote:
>>>> Another quick question about swap: If I have 4 drives, with 512MB
>>>> swap, the system uses all 4 swap partitions, correct? So it's not like
>>>> it'd be going to waste? I'd have a total of 2 GB swap?
>>>
>>> Well, yes. =C2=A0If you just declare those raw partitions to be swap ar=
eas,
>>> that will be the case. =C2=A0However, doing this is asking for trouble:=
 you
>>> subvert any resilience features obtained by using ZFS with raidz1. =C2=
=A0If
>>> any one of the drives fails, your swap area will break and your system
>>> will probably crash.
>>>
>>> Better to set up two pairs of gmirrors for swap -- the procedure is
>>> described here: http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/Mirror
>>> in section3 "Finish Install." =C2=A0This will effectively give you a ra=
id10
>>> for your swap, with a total size of 1GB.
>>>
>>
>> I'm not sure I understand this. How would that negatively affect the
>> raidz1? The swap isn't in the zpool. I understand the system may crash
>> if the OS was using the swap space and the drive failed. But would you
>> not be able to reboot into a degraded zpool state and still have a
>> usable system?
>>
>
> No -- it means a failed disk can cause your system to crash. =C2=A0That's=
 not
> resilient behaviour. =C2=A0Yes, the data on the ZFS raidz1 should survive=
 the
> crash and the reboot, but the point is ZFS raidz1 should be able to
> survive a disk failure like that /without/ a system crash.
>

Ah! I understand. Thank you for the explanation.



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