I am choosing between two similar models of servers, one of which has software RAID, while the other hardware one.
Servers in question are SYS-E32-1 and SYS-E32-3 from So you Start (an OVH brand) and have similar configuration, the biggest differences being absence/presence of Hyper-Threading and hardware RAID:
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SYS-E32-1: Intel Xeon E3 1225v2 (4c / 4t 3.2 GHz+), software RAID
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SYS-E32-3: Intel Xeon E3 1245v2 (4c / 8t 3.4 GHz+), hardware RAID
There are two hard drives in both of the model, which I'll use as either RAID1 or RAID0 under LVM. I am going to run CentOS 6 and other OS guests on a CentOS 6 host with KVM virtualization. Our normal load is the usual web services.
How much should the performance differ for me? Is hardware RAID worth it or more like a rounding error in this scenario?
Clarification: We are not considering "fake RAID" here; only pure software and hardware RAID.
Best Answer
If you have hardware raid then you'll most probably have a hardware controller with hardware cache on it. If that controller has a BBU (battery that retains the contents of the cache on power loss) then the performance difference will be huge.
Having cache with BBU will speed up most of you things a lot. That's because all disk syncs/fsyncs will be instant, meaning that all disk changes for databases, syslog, filesystem journal, etc will be much much faster and won't need to flush the whole write cache to disk.
Having said that, the above is because of the BBUed cache. I.e. the performance should be equally good if you implement software raid on top of the hardware RAID controller. I.e. if you decide to do SW raid when having a HW raid controller.
Regarding their differences, HW raid is usually hassle free and usually comes with hot-swap-ability. You'll have to test that yourself with SW raid as the underlying hardware may have issues.
AFAIC (and I'm propagating some rumors here) HW raid manufactures dedicate a lot on this and take into consideration disk manufacturers and even specific disk models. They are implementing a number of hacks to overcome issues with disks, both for performance and reliability. On the other hand, SW raid will be always improving with kernel upgrades while OTOH it has been said a number of times that HW raid firmware is really bad.
Finally, HW raid comes usually with some logging meaning that you can look at the logs to figure out if a disk is misbehaving. Then again on SW raid you can just run dmesg or look at syslog.