Hardware RAID or software for ZFS

[Matthew Seaman]

On 11/18/14 15:28, bsd at todoo.biz wrote:
> I would need your help in order to figure out which will be the best in order to setup a server which will be used as a Poudriere server. 
> 
> My question is related to the usage of hardware RAID controller (JBOD) or software based controller (graid) 
> 
> Server we are targeting is a SuperMicro 1018R-WC0R - 1U
> 
> I used to build my server using an HBA such as LSI SAS 9207-8i or LSI SAS 9201-16i
> Then I’ll configure the HBA as JBOD so that disks can be presented correctly to the system so that we can build our ZFS FS on top of that. 
> 
> 
> My sysadmin suggested me to get rid of the HBA and use direct connectivity and Graid. 
> 
> 
> I would like to have some feedback on various aspects : 
> 
> 1. performance 
> 2. usability 
> 3. problem one might have encountered
> 

OK -- Your sysadmin is correct about the direct connectivity thing, but
graid?  Seriously?  That's an option for really cheap and some might say
quite nasty pseudo-raid things you get on some desktop hardware.  If
you're going to be building a significant number of packages with any
regularity, then you're going to need something better than that.

The LSI HBAs you suggest are known to work well with FreeBSD.  If you're
going to be using ZFS -- which is really a no-brainer for a poudriere
box, as poudriere has a lot of functionality built around cloning and
snapshotting and other things that come naturally to ZFS[*] -- well, in
that case, ideally you want ZFS to have direct access to the disk devices.

With LSI, when they say 'JBOD' this direct access is generally what they
mean -- although depending on the precise model you get, you may need to
flash the device with different firmware to get the characteristics you
want.  Some other RAID controller manufacturers essentially give you a
load of single-disk RAID-0 devices, so there's still a layer of RAID
controller stuff between ZFS and the disk.  That isn't the kiss of death
to the idea of building a zpool from it, but it's less optimal.

On the three aspecs you mention:

   performance depends very much on the precise type of disk hardware
you specify, how you configure the zpool (for instance, will you be
using ZIL or ARC devices?) and on having enough RAM in the system to
provide an effective buffer-cache for all those ZFS filesystems.

   usability.  I'd say ZFS is pretty usable.  Once it's set up, you
don't really need to interact with things at the level of the HBA.  It
just works.

   problems: this depends very much on the details of what you're trying
to do.  But IMHO you're on the right track with what you've described so
far.

	Cheers,

	Matthew

[*] Although poudriere does now work on UFS as well and has done for a
year or so.





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