How many Hard drives can i connect to this Raid Card?

[ulteriormotive]

This is a custom server, not being built into a Server Chassis. I'm DIY'ing a computer tower and i want to install a RAID into this tower for my home server.

This is the Card
LSI MegaRAID SAS 9261-8i
http://www.avagotech.com/products/server-storage/raid-controllers/megaraid-sas-9261-8i#overview

It says on the product page that...
2 x SFF-8087 mini-SAS

but then it also says...
Devices Supported Up to 128 SAS and/or SATA devices

The only type of cable i found that would work for me is this...
http://www.amazon.com/HighPoint-Internal-Mini-SAS-SFF8087-Int-MS-1M4S/dp/B001L9DU88
Thats a 1 x 8087 to 4 x SATA so looking at that, i can only connect 8 hard drives to this RAID card using both 8087 ports.

MY QUESTIONS:
How can i connect more than 8 SATA HD's into this raid card?
What device do i have to buy to be able to help me do this?
Do i have to buy a backplane of some sort?

Additional INFO,
- All WD RED 4TB
- hoping to have 10 to 12 HD's total
- Raid 5 or 10
- One raid for data and one raid for backup of that data

 

[kanewolf]

You would use a SATA port multipler -- https://en.wikipedia.org/wiki/Port_multiplier

 

[drtweak]

You could go with a Port Multiplier but what you really want is a SAS Expander.

Differnece - Port Multipliers is 1) SATA only which is fine since you are only using SATA drivers but if you ever get SAS drives it won't work 2) You can only do 4 Drives Max per connection (So it would be 40 drives max. 5 Drives time 8 SATA connectors you get) 3) Slower speeds since you have 2-5 drives going over a single SATA connection 4) The RAID is typically NOT a hardware RAID but a software RAID which then if you do a RAID 5 all the RAID fuctions are now on the CPU and not the RAID card slowing the system down all together and 5) From what I have read it requires a SAS expander and not a Port Multiplier

For the SAS Expander you benifit from 1) Actual Hardware RAID for ALL drives 2) You get up to the full 128 Hard drives 3) The bandwith is more load balanced than a Port Multiplier 4) You get SAS capibility if you use SAS Drives.

Now that is the difference. Now the Pros and Cons

Port Multipliers

Pros - Cheaper, easier to use, less parts
Cons - Slower, Software RAID, Drive limit,

SAS Expanders

Pros - Faster, Hardware RAID
Cons - More expensive (Almost twice as much in some cases for hard drive enclosures), requires a seperate SAS Expander for each bay (Usually included when you by the drive Bay)

The one thing i would double check and make sure is that it does support 4TB drives. I don't see why it shouldn't but you never know.

Here is a chart for the different things

http://www.sasexpanders.com/vs/

 

[ulteriormotive]

...really want is a SAS Expander.

I figured that's something along the lines of what I'd need.
Do i need a SAS expander along side a RAID Card (Does the expander Replace a Raid card)?

This is one Expander card that i found...
http://www.newegg.ca/Product/Product.aspx?Item=N82E16816117207&cm_re=sas_expander-_-16-117-207-_-Product
Is this what where talking about here?

If so, This one has...
6 x SFF-8087

so realistically, can i connect 24 hard drives to this using this cable?
http://www.amazon.com/HighPoint-Internal-Mini-SAS-SFF80

This is the furthest I've ever gotten in the years I've been dreaming this thing up, that's why I love this community.

...You get SAS capibility if you use SAS Drives.

Pipe dream, never happening, im small time, not necessary.

 

[drtweak]

a SAS Expander runs alongside the RAID card. If it is all going in one PC then it goes int he same PC. If you get like an external enclosure you would need an expander that goes inside the enclosure. And pretty much what id does is you use connect one of the SFF-8087 to one of the other SFF-8087 ports on the SAS Expander. Then you have the other 5 SFF-8087 ports to go out to 4 drives each giving you 20 Drives. You can't connect both SFF-8087 from the RAID to the expander though.

 

[ulteriormotive]

a SAS Expander runs alongside the RAID card. If it is all going in one PC then it goes int he same PC. If you get like an external enclosure you would need an expander that goes inside the enclosure. And pretty much what id does is you use connect one of the SFF-8087 to one of the other SFF-8087 ports on the SAS Expander. Then you have the other 5 SFF-8087 ports to go out to 4 drives each giving you 20 Drives. You can't connect both SFF-8087 from the RAID to the expander though.

Thank you
Yes everything will be in one PC at the end.

So, recap
LSI MegaRAID 9261-8i (for sure)
1 x SFF-8087 = breakout cable to 4 x sata
1 x SFF-8087 = Intel RES2SV240 Raid Expander Card
Intel RES2SV240 Raid Expander Card (potential, need more research)
1 x SFF-8087 = direct plug in from LSI MegaRAID card
1 x SFF-8087 = breakout cable to 4 x sata
1 x SFF-8087 = breakout cable to 4 x sata
1 x SFF-8087 = breakout cable to 4 x sata
1 x SFF-8087 = breakout cable to 4 x sata
1 x SFF-8087 = breakout cable to 4 x sata

Giving me a total of 24 potential HD's
Is that correct? i believe it is



--HYPOTHETICALLY SPEAKING-
If the top is correct and if i wanted to add some more HD's would i just plug in the second SFF-8087 thats on the raid card to another Intel RES2SV240, i know that thought is overkill but im just curious is all.

 

[marko55]

You're absolutely correct, and I can tell you first hand that the Intel RES2SV240 will work with the LSI card. You can also daisy chain the Intel SAS expanders off each other. This is how you get up to the 128 drives your RAID card can drive.

A few things that you need to keep in mind in regards to your design though. Granted these would be more future-proofing considerations based on your actual current number of drives so this is more in response to the "potential of 24 HDDs."

1) Bandwidth to the RAID card for the array(s) its driving. Using a single SFF8087 connector to the expander(s) provides about 2GB/s. If you're running all these drives in a single RAID 5 (see point 3 about concerns w/this too...), and all your drives can do say 175MB/s, then you've got 20 drives connected to your SAS expander that can potentially move 3.5GB/s of transfer speed, but they only have 2GB/s of bandwidth from the expander to the RAID card. With the number of drives you're using and the speed of WD reds you should be just fine.

2) Bandwidth of the PCIe 2.0 x8 interface of the card. First, make sure you have 8 lanes available to the card. That interface caps around 4GB/s to the mobo. Again, all good for your (current) scenario.

3) You don't really want to put more than 16 drives in any array, and when you get to a certain number of drives (varies by builder) you want to jump from RAID-5 to RAID-6 to protect yourself. There are even more different schools of thought on this decision to depending on your backup scenario.

IMO, with groups of 6 drives, RAID-5 with write-back enabled on your card, especially since you're backing up your data. RAID-10 eats space & gets pricy. With write-back on a RAID-5 you'll get great write performance with that card. The LSI card will let you force write-back even without a battery. You'll get great performance on those arrays. Read-ahead, always write-back, cached IO, 64K stripe, it'll boogy. I would suggest grabbing the battery for your card or at a minimum get a small UPS for your computer.

 

[drtweak]

^^^ Yup.

Also what I would do is if the next Expander card you get I would plug it in to the OTHER 8087 port on the LSI card and then plug your 4 Existing drives into that new expander. If you just run the expander off the expander then you are adding more drivers to an already maxed out connection where as if you add another card to the other 4 ports you now get another 2GBps to use for your next RAID