Date: Mon, 13 Jul 2009 10:46:26 -0700 (PDT) From: Richard Mahlerwein <mahlerrd@yahoo.com> To: Free BSD Questions list <freebsd-questions@freebsd.org> Subject: Re: ZFS or UFS for 4TB hardware RAID6? Message-ID: <78927.1741.qm@web51001.mail.re2.yahoo.com>
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--- On Mon, 7/13/09, Richard Mahlerwein <mahlerrd@yahoo.com> wrote: > From: Richard Mahlerwein <mahlerrd@yahoo.com> > Subject: Re: ZFS or UFS for 4TB hardware RAID6? > To: "Free BSD Questions list" <freebsd-questions@freebsd.org> > Date: Monday, July 13, 2009, 1:29 PM > --- On Sun, 7/12/09, Maxim Khitrov > <mkhitrov@gmail.com> > wrote: > > > From: Maxim Khitrov <mkhitrov@gmail.com> > > Subject: ZFS or UFS for 4TB hardware RAID6? > > To: "Free BSD Questions list" <freebsd-questions@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
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