LSI MegaRAID Backplane 36 HDD

[corilde]

I have a 847E16 supermicro with 36 bay HDD. I bought a two LSI cards, but I don't know how connect the two backplane, because when power on the system, I have a message "LSI MegaRAID Number of disks exceeded the maxium supported count of 32 disks. Please remove the extra drives and reboot system to avoid losing data." I can understand that this message appears when only have a one card, but with two, I think that I can use 64 units, but I'm sure that I don't connect correctly the two backplanes and I don't kwow how do it.

Any help? THANKS

 

[jgreco]

LSI MegaRAID RAID cards have a limit as to the number of drives supported. This is done so that they can sell the same hardware at a higher price without the limit. The limit is per card, not aggregate across your system.

Note that it's great that you hit this limit, because it gives me the chance to warn you off of a misadventure. You need to get rid of the RAID cards and use HBA's instead. This is nonoptional; see

What's all the noise about HBAs, and why can't I use a RAID controller?

1) An HBA is a Host Bus Adapter. This is a controller that allows SAS and SATA devices to be attached to, and communicate directly with, a server. RAID controllers typically aggregate several disks into a Virtual Disk abstraction of some sort...

www.truenas.com

 

[corilde]

Thanks for your reply.

Then, the limit is the RAID CARD, so... that I have two RAID CARD, I can't use more 32 HDD because these RAID CARD limit, true? Is not possible use 24 hdd with one RAID CARD (connect with one backplane) and 12 hdd with the other RAID CARD (connect to the other backplane)?

Thanks again!

 

[jgreco]

You need ZERO RAID cards. Remove both RAID cards. Replace with HBA. See the article I linked.

 

[corilde]

You need ZERO RAID cards. Remove both RAID cards. Replace with HBA. See the article I linked.

THANK YOU SO MUCH! I bought today a HBA and I replace two RAID CARDS and voila, works. 36 HDD.

One question: if I want to expand to more units, is enough with this HBA?

 

[jgreco]

There are two things to know:

There is a limit per LSI HBA controller.

Code:

# sas3ircu 0 display
Avago Technologies SAS3 IR Configuration Utility.
Version 16.00.00.00 (2017.04.26)
Copyright (c) 2009-2017 Avago Technologies. All rights reserved.

Read configuration has been initiated for controller 0
------------------------------------------------------------------------
Controller information
------------------------------------------------------------------------
  Controller type                         : SAS3008
  BIOS version                            : 8.37.00.00
  Firmware version                        : 16.00.10.00
  Channel description                     : 1 Serial Attached SCSI
  Initiator ID                            : 0
  Maximum physical devices                : 255
  Concurrent commands supported           : 3072
  Slot                                    : Unknown
  Segment                                 : 0
  Bus                                     : 11
  Device                                  : 0
  Function                                : 0
  RAID Support                            : No
------------------------------------------------------------------------

This one has a 255 device limit. Some have less. However, there are practical factors to the SAS topology. You are using SAS expanders if you have a 36-bay chassis, please feel free to go over and see the SAS Primer in the resources. Depending on how you've hooked things up, you may be limited to 12Gbps or 24Gbps to a backplane, which may be fine for HDD's in many cases, but once you start stringing up lots of drives, you start to get contention.

Your ideal case is probably where you have an SAS link to each expander. For external expanders in a JBOD, an HBA with external connectors will let you hook up more drives without slowing down what you already have inside the server.