Setting up ZFS - Filesystem Properties and Installing on Root
apseudoutopia at gmail.com
Thu Nov 24 19:29:43 UTC 2011
On Thu, Nov 24, 2011 at 2:26 PM, Matthew Seaman
<m.seaman at 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 at 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. If you just declare those raw partitions to be swap areas,
>>> that will be the case. However, doing this is asking for trouble: you
>>> subvert any resilience features obtained by using ZFS with raidz1. If
>>> 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." This will effectively give you a raid10
>>> 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. That's not
> resilient behaviour. Yes, 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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