what happens to pool if ZIL dies on ZFS v14

[jhell]

On 09/17/2010 13:09, Freddie Cash wrote:
> On Fri, Sep 17, 2010 at 9:47 AM, Gil Vidals <gvidals at gmail.com> wrote:
>> First, let me say that I'm receiving excellent input from the FreeBSD
>> community. I'm new to FreeBSD and ZFS and this mailing list has been very
>> helpful.
>>
>> I'm running ZFSv14 on FreeBSD 8.1 AMD64 with 8GB of DDR3 RAM with two SSDs -
>> one for the ZIL and the other for the L2ARC cache.
>>
>> zambia# zpool iostat -v 1 1
>>                     capacity     operations    bandwidth
>> pool               used  avail   read  write   read  write
>> ----------------  -----  -----  -----  -----  -----  -----
>> tank              6.57G   921G      0     11   116K   438K
>>  mirror          6.57G   921G      0      5   116K   229K
>>    label/disk1       -      -      0      3  57.9K   229K
>>    label/disk2       -      -      0      3  57.8K   229K
>>  label/zilcache   136K  59.5G      0      6     17   209K
>> cache                 -      -      -      -      -      -
>>  label/l2cache   59.6G  8.50K      0      0  31.5K  48.9K
>> ----------------  -----  -----  -----  -----  -----  -----
>>
>> Observing the ZIL Cache, I see it being used very sparingly. And now that I
>> know the SSD slog must be mirrored in ZFS < v19, I think the best course of
>> action (assuming I'm not buying more equipment) is to mirror the ZIL SSD and
>> abandon the L2ARC altogether. Won't RAM be used for L2ARC instead?
> 
> The ZIL is only used for synchronous writes, and does not need to be
> very large.  I forget the formula for determining the exact size of a
> ZIL (something along the lines of the max amount of data you can write
> in 30 seconds), but it's rarely more than 4 GB and usually in the 1-2
> GB range.
> 
> If possible, you'd be better off rebuilding your pool like so:
>   mirror disk1 and disk2
>   slice both SSDs into two:  4-8 GB for ZIL, rest for L2ARC
>   mirror zilcache1 zilcache2
>   add l2cache1 l2cache2 (don't mirror them)
> 
> That way, you have a mirrored ZIL, and double the L2ARC.  However,
> since it takes around 270 bytes of RAM for every object in the L2ARC,
> you'll want to make sure you have lots of RAM to manage it (or,
> possibly, make 3 slices on the SSDs and use the third for swap?).
> 
http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide#Disabling_the_ZIL_.28Don.27t.29

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 jhell,v