On Jan 28, 2013, at 3:43 PM, Artem Kuchin wrote:

> I have to made a decision on choosing a dedicated server.
> The problem i see is that while i can find very affordable and good options 
> they do not
> provide hardware raid or even if they do it is not the best hardware for 
> freebsd.

I prefer SW RAID, specifically ZFS, for two very large reasons:

1) Visibility: From the OS layer you have very good visibility into the health 
of the RAID set and the underlying drives. All of the lower end HW RAID 
solutions I have seen require proprietary software to "manage" the RAID 
configuration, usually from the physical system's BIOS layer. Finding good OS 
layer software to monitor the RAID and the drives has been very painful. If you 
don't know you have a failure, then you can't do anything about it and when you 
have a second failure you lose data. Running a HW RAID system and not being 
able to issue a simple command from the OS and see the status of the RAID 
scares me.

2) Error Detection and Correction: HW RAID relies on the drives to report read 
and write errors. With UNCORRECTABLE error rates of 10^-14 and 10^-15 and LARGE 
(1 TB plus) drives you are almost guaranteed to statistically run into 
UNCORRECTABLE errors over the life of a typical drive. ZFS has end to end 
checksums and can detect a single bad bit from a drive, if the set is redundant 
it can recreate the correct data and re-write it, effectively correcting the 
bad data on disk.

NOTE: Larger, more expensive HW RAID systems address both of the above issues, 
but at a much higher cost in terms of money and management overhead.

DISCLAIMER: I have been managing mission critical, cannot afford to lose it 
data under ZFS for over 5 years, with no loss of data (even with some horribly 
unreliable low cost HW RAID systems under the ZFS layer... if we had not used 
ZFS we would have lost data multiple times).  

--
Paul Kraus
Deputy Technical Director, LoneStarCon 3
Sound Coordinator, Schenectady Light Opera Company

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