Teach me about SAS Backplanes

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pcm81

Senior member
Mar 11, 2011
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Good evening all.
I have a quick question about using SAS backplane. I am about to buy a server case to build a Xeon E5 based server. Something like: "Rosewill Server Chassis/Server Case/Rackmount Case, 4U Metal Rack Mount Server Chassis with 12 Hot Swap Bays". This will be a VM / Storage server for a home use. What should I expect to have to configure with SAS hot swappable backplane in the case? Do I need a SAS or SATA port on motherboard? Will the system see all drives as JBOD? Can I connect the SAS backplane to a raid controller (SAS or SATA?) with a single cable and set it up as RAID5 or will Raid controller need to see drives on different controller ports?

I will be using SATA drives in the server, would like to set them up as either a RAID or JBOD. Raid for redundancy, not going after the full throttle speed, hence a single SAS/SATA link is fast enough. Also, will the SAS uplink work at full 6Gbps if I am reading/writing to multiple SATA2 drives in JBOD config even though each drive can not read/write at 6Gbps or is the communication bandwidth limited to one drive at a time?



Thanks ahead
 
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XavierMace

Diamond Member
Apr 20, 2013
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Step 1: Don't buy a Rosewill case.

Seriously, just don't.

To give more accurate information regarding connection, we would need to know the specific model. There's different types of backplanes. Some need individual connections for each drive, some just have a single SFF-8087 (or similar) connection.

In regards to how the drives will be seen, the backplane is just providing ports. How they will be seen is entirely dependent on what the backplane is plugged into.
 
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therealnickdanger

Senior member
Oct 26, 2005
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XavierMace said:
Step 1: Don't buy a Rosewill case.
Click to expand...

Step 2: don't listen to XavierMace.

;)

I've got a couple Rosewill 4U cases with 12 drive bays on backplane. They've been working great for years. No complaints other than weight and some sharp edges. Keep in mind that I was also able to get them for under $150 each on different sales. There may be better cases around its full MSRP.

A backplane in this sense is just a middleman between your drives and your SATA/SAS controller. Plug your controller(s) into the backplane ports, then slide your drives into the hot swap bays. The backplane doesn't care how you configure your drives (JBOD, RAID, etc.), it's just a passthrough to make physical drive installation/removal better.
 
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Noo

Senior member
Oct 11, 2013
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You should really know what you are doing before buying all of that. 12 bay hot swap case and you don't know how a backplane works? I'm guessing you're not going to go all out and buy 12 4tb HDd to fill the server.
 
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Noo

Senior member
Oct 11, 2013
389
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No mechanical HDD is going to saturate the 6gbs sata3. No point in sas controller if you are going to use sata drives (have you check the prices on 4tb SAS drives? Multiply that by 12 I guess).
 
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XavierMace

Diamond Member
Apr 20, 2013
4,307
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therealnickdanger said:
Step 2: don't listen to XavierMace.

;)

I've got a couple Rosewill 4U cases with 12 drive bays on backplane. They've been working great for years. No complaints other than weight and some sharp edges. Keep in mind that I was also able to get them for under $150 each on different sales. There may be better cases around its full MSRP.
Click to expand...

There's a reason they are cheap. They are shitty rackmount cases. I've had two Rosewill's, a handful of Norco and Chenbro, and a buttload of Supermicro's. If I was so cheap I would only spend enough money for a Rosewill and nothing else, I'd just not buy a rackmount case as you'd get far more for that amount of money with a regular tower case. The Norco's weren't spectacular, but still better than Rosewill.
 
frowertr

frowertr

Golden Member
Apr 17, 2010
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XavierMace said:
That's not necessarily true. It depends on the backplane he's plugging into.
Click to expand...

Correct. A six disk RAID 10 would could saturate a single 6Gbps link with no problem during a heavy read.

Most backplanes, however, don't tie all the drives into a single physical SAS/SATA 6Gbps link. That is why we would have to know a specific model number to tell you how it works.
 
master_shake_

master_shake_

Diamond Member
May 22, 2012
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Noo said:
which mechanical HDD that's capable of read/write 550MB/s? I'll throw away all of my ssd :/
Click to expand...


this is a 12 2tb seagate raid 6

2b85f969_3434A2E5-4B94-447E-9D51A01B0A3E7A74.jpeg
 
frowertr

frowertr

Golden Member
Apr 17, 2010
1,372
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Noo said:
which mechanical HDD that's capable of read/write 550MB/s? I'll throw away all of my ssd :/
Click to expand...

Using RAID 10, for example, disk reads are cumulative for the entire array. So lets say you have a 7200K drive with a disk performance of 200 MBps which is pretty common for that speed. If you had four identical disks in the RAID 10 array (that is the minimum required for RAID 10), then that would give you a theoretical read speed of 800MBps for the entire array if all it was doing was reading and not writing.

Considering a SATA/SAS 3 link is approx 760MBps, you could saturate a single link with just four drives in RAID 10.

This is another reason why One Big RAID 10 (OBR10) is becoming common place in Enterprise use. If you don't break your spindles up, you get better read and write performance compared to multiple smaller arrays. But I digress, that is another topic...
 
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pcm81

Senior member
Mar 11, 2011
597
13
81
Thank you all for the replies. The reason for a 12 bay case is for future expandability. The machine will start as a VM server (to replace my current raspberry Pi2) and eventually grow to storage / back-up server to supplement my current Synology DS1515+. Basically I have never had a reason to use SAS before, hence the questions about how it works vs regular point to point SATA connections... The build is not intended for enterprise environment, hence I will be using SATA drives. The main reason for choosing this case is b/c it's cheap. With xeon e5 +RAM +Mobo I'd like to keep it under $500, then add $200 case and add drives slowly as money allows.
 
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rchunter

Senior member
Feb 26, 2015
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master_shake_ said:
i use a norco 4224 and a norco 4020 with intel sas expanders an an lsi 9260-4i.

if i were to do it again i'd use a supermicro 24 bay.

this one comes with a 30 day warranty, rails, power supplies, and has 36 bays.

for 600 dollars.

although you will need to add hardware, but apparently fb is selling off xeons for cheap.

http://www.ebay.com/itm/SuperMicro-...982872?hash=item41a51c80d8:g:ClMAAOSwuAVWy49v
Click to expand...


As far as I can tell this comes with SAS-1 backplanes. No thanks....
 
master_shake_

master_shake_

Diamond Member
May 22, 2012
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rchunter said:
My bad, yeah it's a steal for 600 dollars.
Click to expand...


no you are right i'm wrong.

the backplane is the expander and the expander is 6gbps.

thought you were talking about the norcos.

but yeah it is 6gbps.

sorry.

if i were in america i'd have 2 by now. lol.
 
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rchunter

Senior member
Feb 26, 2015
933
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pcm81 said:
LOL yeah... that is definitely not the price point I am looking for....
Click to expand...

I'm really tempted at $600, but I don't think I would ever use 36 bays. I think I'd rather have just 24 bays and use my own 6GB HBA controllers and not have to use an expander. Also with that chassis you can't use full height cards in it, only half height.
 
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pcm81

Senior member
Mar 11, 2011
597
13
81
My original question was about a small low end chassis to build a VM server in and have 8-12 bay expandability for future raid...

If I am using SATA drives in a chassis with SAS backplane, do I need SAS or SATA controller on MOBO?

Can the drives be separated between a MOBO and raid controller card with say 1 drive being boot drive, while others being a raid setup or will the SAS backplane require all drives to be connected to the same controller?
Would a raid controller with a single SAS port be enough or do I need as many ports as there are drives if I do not care about speed... I won't saturate 6Gbps....
 
frowertr

frowertr

Golden Member
Apr 17, 2010
1,372
41
91
pcm81 said:
My original question was about a small low end chassis to build a VM server in and have 8-12 bay expandability for future raid...

If I am using SATA drives in a chassis with SAS backplane, do I need SAS or SATA controller on MOBO?
Click to expand...

We still don't know what backplane you are looking at. Typically, SAS backplanes are going to have one or more mini-SAS connectors (SFF-8087) on the backside of them. So, for instance, a 4 drive SAS backplane may only have one mini-SAS connector on the back. This is because the SFF-8087 connector is x4 wide which means one single cable can handle four physical drives and each drive will have a full SAS 12Gbps/6Gbps link depending on the controller/backplane. This cable would run from your backplane to your HBA/RAID controller/motherboard SAS connector.
 
frowertr

frowertr

Golden Member
Apr 17, 2010
1,372
41
91
pcm81 said:
Can the drives be separated between a MOBO and raid controller card with say 1 drive being boot drive, while others being a raid setup or will the SAS backplane require all drives to be connected to the same controller?
Would a raid controller with a single SAS port be enough or do I need as many ports as there are drives if I do not care about speed... I won't saturate 6Gbps....
Click to expand...

There are all kinds of ways to do this depending on what controller/backplane you purchase.

First, what hypervisor are you wanting to use? If it's ESXI you are basically stuck with hardware RAID and will need a hardware RAID controller so you can forget about using a motherboard SAS connector if its RAID you want.
 
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