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LSI2008 and Raid-5

pillagenburn

pillagenburn

[H]ard|Gawd
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So I've searched around on this and found that people generally don't feel as though the LSI2008 and RAID-5 are a good combination due to write issues of various types (performance, reliability etc).

My setup (six 2gb Hitachi drives, quad 8-core Opterons, 80 gigs of RAM, SSD for primary storage for OS, Hyper-V OS'es etc) are going to be more read-heavy from the RAID-5 array as these will be for streaming video to Extenders etc.

Questions:

What are the issues surrounding enabling write caching on a RAID-5 array using this controller? Are they limited to issues arising from power failures? I've got 80 gigs of RAM and it will be attached to a good UPS, so I don't expect power disruptions to be an issue. So other than power disruptions, what are the issues with using the cache-less LSI2008?

I'd just like to hear folks' opinions on using this controller in this configuration and for my uses (6-drives, LSI2008 controller and RAID-5).
 
The LSI2008 is a bit to weak for parity calculations. That is the main reason the RAID5 performance is not that good.
I would rather use software RAID, and RAID6 with the size of the drives you use.
 
omniscence said:
The LSI2008 is a bit to weak for parity calculations. That is the main reason the RAID5 performance is not that good.
I would rather use software RAID, and RAID6 with the size of the drives you use.
Click to expand...

a bit too weak as in the actual processing horsepower of the LSI2008 is weak?
 
Yes. IMHO it is fine for RAID0 and RAID1, but as soon as parity is involved it delivers suboptimal throughput. Today the only strong point of hardware RAID cards is writeback caching with power-loss protection, which enables very good write latencies. The host processor can easily do the parity calculations without generating any noticeable load.

I used to believe that the LSI2008 does not do the XOR itself but offloads it to the host, but someone here said that it does. Without an own RAM for parity calculations, it can only work on a small dataset and not load and process multiple stripes at the same time.
 
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So I'm trying to decide what I want to do.. I want RAID5/6, but I'm debating whether getting a cheap-o 3gbps hardware card with some cache on it is the better idea here...

I guess the other question I have is would six 5400 RPM Hitachi drives overwhelm a 3gbps card?
 
I'm seeing these HP P410 cards are farily plentiful and not that expensive (plus options for RAM expendability)...

anyone have experiences with these? It seems I shouldn't skimp on the RAID card...

edit: nevermind, crappy write performance.
 
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pillagenburn said:
I'm seeing these HP P410 cards are farily plentiful and not that expensive (plus options for RAM expendability)...

anyone have experiences with these? It seems I shouldn't skimp on the RAID card...

edit: nevermind, crappy write performance.
Click to expand...

stay away with HP Raid Card.
HP Card is so picky!!!!!
I only have one motherboard can detect correctly: Asus matx AM2.

Writing performance should be ok, when battery backup and memory are installed, set ratio 75% read and 25% write.

get dell LSI HW raid card or IBM LSI HW raid card..
 
As others have pointed out the lack of memory on the sas2008 is the main (perhaps only?) culprit for suboptimal raid5. If you want something inexpensive that should perform well for raid5 then perhaps a sas2108 card would be more ideal. You can find OEM versions from server pulls on ebay quite cheap, for example I believe I saw an IBM ServeRAID M5015 for $149 or best offer yesterday.

Yes, here it is
http://www.ebay.com/itm/46M0851-IBM...sk_Controllers_RAID_Cards&hash=item19f0d4af3f

This thread over at servethehome.com has a very nice compilation of the various LSI chips, OEM counterparts, and capabilities.
https://forums.servethehome.com/ind...and-hba-complete-listing-plus-oem-models.599/
 
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I just bit the bullet and purchased a LSI 8888ELP w/o battery for $40 on ebay... I got tired of screwing with it and wanted something inexpensive and effective - I see good performance numbers on these (despite being 3gbps cards).

I'll look at upgrading to 6gbps later if I really feel like it...

edit: wish the batteries for these things weren't so crazy expensive though :(
 
In my experience the trick to getting things cheap is to find the OEM equivalents and search for those. An LSI 9211-8i from newegg might run you $400 (no idea, just guessing) but an IBM ServeRAID M1115 on ebay (used) will cost $100. Hell, I got both of mine new from amazon for $90 each but I got real lucky.

My point is, there is only one physical BBU for that card you mentioned, but I'm sure you'll find a dozen different makes and models from HP, Dell, IBM, etc. It's just a matter of mapping which is which and then finding the good deals on them!
 
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