to gmirror or to ZFS

[krad]

You would in theory as from what i remember every zfs filesystem takes up
64 kb of ram, so the savings could be massive 8)


On 16 July 2013 10:41, Shane Ambler <FreeBSD at shaneware.biz> wrote:

> On 16/07/2013 14:41, aurfalien wrote:
>
>>
>> On Jul 15, 2013, at 9:23 PM, Warren Block wrote:
>>
>>  On Mon, 15 Jul 2013, aurfalien wrote:
>>>
>>>  ... thats the question :)
>>>>
>>>> At any rate, I'm building a rather large 100+TB NAS using ZFS.
>>>>
>>>> However for my OS, should I also ZFS or simply gmirror as I've a
>>>>  dedicated pair of 256GB SSD drives for it.  I didn't ask for SSD
>>>>  sys drives, this system just came with em.
>>>>
>>>> This is more of a best practices q.
>>>>
>>>
>>> ZFS has data integrity checking, gmirror has low RAM overhead.
>>> gmirror is, at present, restricted to MBR partitioning due to
>>> metadata conflicts with GPT, so 2TB is the maximum size.
>>>
>>> Best practices... depends on your use.  gmirror for the system
>>> leaves more RAM for ZFS.
>>>
>>
>> Perfect, thanks Warren.
>>
>> Just what I was looking for.
>>
>
> I doubt that you would save any ram having the os on a non-zfs drive as
> you will already be using zfs chances are that non-zfs drives would only
> increase ram usage by adding a second cache. zfs uses it's own cache
> system and isn't going to share it's cache with other system managed
> drives. I'm not actually certain if the system cache still sits above
> zfs cache or not, I think I read it bypasses the traditional drive cache.
>
> For zfs cache you can set the max usage by adjusting vfs.zfs.arc_max
> that is a system wide setting and isn't going to increase if you have
> two zpools.
>
> Tip: set the arc_max value - by default zfs will use all physical ram
> for cache, set it to be sure you have enough ram left for any services
> you want running.
>
> Have you considered using one or both SSD drives with zfs? They can be
> added as cache or log devices to help performance.
> See man zpool under Intent Log and Cache Devices.
>
>
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