Software PCI-e 4x(+) Raid?

Mercutio · 3 Apr 2008 at 17:42

Sorry for all the questions today!

Considering dual/quad core has plenty of spare juice to run the XOR raid 5 calculations is there any particular need to move to something like the rocketraid cards?
What advantage do they have over using a semi-hardware or just a random 4/8 port PCI-e SataII/Raid card? They dont seem to have the memory for caching (and aren't likely to benefit much from it either as not in a continual i/o environment where you'd usually see raid 5 used?) so apart from taking the load off the processor what other advantage is offered?

If the answer is "little" can anyone recommend a semi-hardware 4 or 8 port PCIe card? I find doing it purely in software in windows tends to be a bit of a chore (perhaps I havent done a pure software raid long enough to see) so semi-hardware would be prefered.
Selling this to myself on the premise that quad core = £120, rocketraid = £160+

Obviously if write operations are run MUCH faster on a hardware card ill be swayed back that way.

rpstewart · 3 Apr 2008 at 18:25

It's not just a case of how much grunt the processor has, how well written the drivers are will have more of an impact. Personally I wouldn't try RAID5 on anything less than a RocketRAID 2320 and preferably either a RR 3xxx or an Areca 1220.

The 2320 isn't a full on hardware card, it still offloads some stuff to the CPU but I can get writes of 80MB/s and that's on an 8 disk array so 7 lots of XORing per write.

The general rule of thumb figure for software solutions like the normal southbridge controllers is about 20MB/s although the ICH9R is meant to be a fair bit better but I've not seen any figures. You still have the usual disadvantages of motherboard controllers as well - lack of portability etc.

Mercutio · 4 Apr 2008 at 11:50

In that case would I be correct in thinking that for cost/performance raid 10 (strip+mirror or mirror+strip, whichever way around it does it thats different to raid 0+1) would generally be the best performance/price?

Considering 4 largish drives = ~£280 + 4 port Hardware raid 10 ~£55 = ~£335

Vs

Rocketraid ~£180 + 3 largish drives (for same capacity as the above) ~£210 = ~£390 with a probable performance loss over the raid 10.

Im basically after around 1TB of storage that suffer a drive loss without data loss problems so the raid 10 option seems slightly better in my case (Obviously not for yourself with much higher storage requirements).

rpstewart · 4 Apr 2008 at 13:27

Generally 4 disk RAID10 will be a better value proposition than a decent 3 disk RAID5 setup, especially if you run it from a motherboard controller.

Mercutio · 4 Apr 2008 at 17:02

Excellent, thanks.

As another option im considering (sorry to be going in so many random directions!) I see several external raid boxes. Some support Sata2 drives to Esata. If this was hooked up to a Sata2 connector on the mainboard would it give up to 300MB/sec or would it depend on the controller in the raid box (so in the case of a box that doesn't mention having a Esata2 connector id be capped at 150MB/sec)?

If it depends on the controller does anyone know a make/model for a suitable box? At the moment id want it for Raid1 if I was going this route so the extra throughput wouldn't be needed but as most of these enclosures support both it would a nice option to have further down the road for raid0.

If anyone knows of a 2xsata/sata2 to Esata2 controller that would likely help with my search.

rpstewart · 4 Apr 2008 at 17:38

The speed will depend on the disk. There isn't a SATA drive out there which can saturate a 150MB/s link, let alone a 300MB/s one.

I don't recall seeing a multi-drive eSATA box with anything other than just a backplane in it. They all have multiple eSATA ports on the back, normally single ones but occasionally a 4 channel miniSAS connector. You then need to get the right cable for the box and controller.

Mercutio · 4 Apr 2008 at 18:58

Well aware your average (IDE/Sata) drive is lucky to push 90MB/sec so wont even touch sata port speeds. There are enclosures that do 2 drives to a raid controller to a single Esata (just google for esata raid enclosure, set it to UK only), my angle was at this point theres a chance a pair of drives in raid0 could exceed Sata port speeds.

I think my problem was not realising Esata was already specced to 300MB/sec.

rpstewart · 4 Apr 2008 at 19:13

Personally if I was worrying about performance I wouldn't be trusting that sort of device, I'd go for a proper 4 port box and do the RAID stuff back at the PC.

marscay · 4 Apr 2008 at 23:35

i don't know why everybody suggests areca, they have a good but overstated reputation (not totally flawless either) and for home use you can get the same performance with cheapers options from 3ware,LSI and others.

personally i wouldn't bother looking at the 2320 highpoint card, u may as well stick to using onboard really - either plump up for a dedicated hardware card or onboard ...buying a quasi card like the 2320 is just dead money.

anything using the IOP333 will be good enough and you will struggle to max out it's potential until moving to 10+ drives, the IOP341 is a nice processor but most home users will never touch it's power, it's akin to using SLI/Crossfire @ 1024x768 resolution.

i see 200MB/s writes on my system with only 4 5400rpm green power WD drives in raid 5 and my controller cost a total of £80 including battery back up and 512mb ram, you can get great performance with a bit of knowledge.