ZFS or UFS for 4TB hardware RAID6?

[Richard Mahlerwein]

--- On Mon, 7/13/09, Richard Mahlerwein <mahlerrd at yahoo.com> wrote:

> From: Richard Mahlerwein <mahlerrd at yahoo.com>
> Subject: Re: ZFS or UFS for 4TB hardware RAID6?
> To: "Free BSD Questions list" <freebsd-questions at freebsd.org>
> Date: Monday, July 13, 2009, 1:29 PM
> --- On Sun, 7/12/09, Maxim Khitrov
> <mkhitrov at gmail.com>
> wrote:
> 
> > From: Maxim Khitrov <mkhitrov at gmail.com>
> > Subject: ZFS or UFS for 4TB hardware RAID6?
> > To: "Free BSD Questions list" <freebsd-questions at freebsd.org>
> > Date: Sunday, July 12, 2009, 11:47 PM
> > Hello all,
> > 
> > I'm about to build a new file server using 3ware
> 9690SA-8E
> > controller
> > and 4x Western Digital RE4-GP 2TB drives in RAID6. It
> is
> > likely to
> > grow in the future up to 10TB. I may use FreeBSD 8 on
> this
> > one, since
> > the release will likely be made by the time this
> server
> > goes into
> > production. The question is a simple one - I have no
> > experience with
> > ZFS and so wanted to ask for recommendations of that
> versus
> > UFS2. How
> > stable is the implementation and does it offer any
> benefits
> > in my
> > setup (described below)?
> > 
> > All of the RAID6 space will only be used for file
> storage,
> > accessible
> > by network using NFS and SMB. It may be split into
> > separate
> > partitions, but most likely the entire array will be
> one
> > giant storage
> > area that is expanded every time another hard drive
> is
> > added. The OS
> > and all installed apps will be on a separate software
> RAID1
> > array.
> > 
> > Given that security is more important than
> performance,
> > what would be
> > your recommended setup and why?
> > 
> > - Max
> 
> Your mileage may vary, but...
> 
> I would investigate either using more spindles if you want
> to stick to RAID6, or perhaps using another RAID level if
> you will be with 4 drives for a while.  The reasoning
> is that there's an overhead with RAID 6 - parity blocks are
> written to 2 disks, so in a 4 drive combination you have 2
> drives with data and 2 with parity.  
> 
> With 4 drives, you could get much, much higher performance
> out of RAID10 (which is alternatively called RAID0+1 or
> RAID1+0 depending on the manufacturer and on how accurate
> they wish to be, and on how they actually implemented it,
> too). This would also mean 2 usable drives, as well, so
> you'd have the same space available in RAID10 as your
> proposed RAID6.  
> 
> I would confirm you can, on the fly, convert from RAID10 to
> RAID6 after you add more drives.  If you can not, then
> by all means stick with RAID6 now!
> 
> With 4 1 TB drives (for simpler examples)
> RAID5 = 3 TB available, 1 TB worth used in "parity". 
> Fast reads, slow writes. 
> RAID6 = 2 TB available, 2 TB worth used in "parity". 
> Moderately fast reads, slow writes.
> RAID10 = 2 TB available, 2TB in duplicate copies (easier
> work than parity calculations).  Very fast reads,
> moderately fast writes.
> 
> When you switch to, say, 8 drives, the numbers start to
> change a bit.
> RAID5 = 7TB available, 1 lost.
> RAID6 = 6TB available, 2 lost.
> RAID10 = 4TB available, 4 lost.
> 

Sorry, consider myself chastised for having missed the "Security is more important than performance" bit. I tend toward solutions that show the most value, and with 4 drives, it seems that I'd stick with the same "data security" only pick up the free speed of RAID10.  Change when you get to 6 or more drives, if necessary.

For data security, I can't answer for the UFS2 vs. ZFS.  For hardware setup, let me amend everything I said above with the following:

Since you are seriously focusing on data integrity, ignore everything I said but make sure you have good backups!  :)

Sorry, 
-Rich