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This article is a step-by-step guide to configure SAS controller/disk for use in AIX or VIOS logical partition.
I had to configure SAS disks for my work on an AIX partition and found it difficult to locate any “how-to” article on the Internet.
Though i figured out that there was a command “sissasraidmgr” to get this done.
I was sort of convinced that I would have use the complicated command ( yuck ) to get the job done and decided to go through the MAN page for the command line options. To my surprise ( voila ) this is what I found in the Description of the command’s man page ( important sections highlighted for your convenience ) :


       The sissasraidmgr command is used to create, delete, and maintain RAID
       arrays on a Peripheral Component Interconnect-X (PCI-X) or PCI Express
       (PCIe) SAS RAID controller. Attention: See the Power Systems SAS RAID       <<<<<<
       Controllers for AIX reference guide and become familiar with the
       storage management concepts before you run the sissasraidmgr command.
       Attention: The System Management Interface Tool (SMIT) smit sasdam fast     <<<<<<
       path is the preferred method to manage a SAS RAID controller.
       Attention: Service tasks require special training and must not be
       performed by nonservice personnel.

This man page description solved half of my problems :
 A  : It indicated that there was a “Power Systems SAS RAID Controllers” reference guide for AIX. After a quick search in Google i got it from this link : PDF ( SAS RAID Controllers for AIX )
 B  : There is an easier and intuitive SMIT interface to manage the SAS devices 🙂

I went through the required information in the “reference guide” and configured the SAS disks for my use. I highly recommend you to read through the guide for all your work with SAS controllers and SAS disks. Though, i later figured out that there was an IBM Knowledge Center article on it ( though not as comprehensive as the reference guide ) ; here’s the link : Preparing disks for use in SAS disk arrays

 

The rest of this article is my version of a step-by-step ( get-it-done ) guide, to configure your SAS controller and get your SAS disks for use.
[ NOTE : I assume that your logical partition is installed with AIX or VIOS and are not already using these SAS disks ]

 

 1 . To start, get the list of adapters available on the partition ( and grep for sas adapter ). Here I see that my partition has a single SAS adapter.

# lsdev -Cc adapter | grep sas
sissas0 Available 01-00 PCIe3 12GB Cache RAID SAS Adapter Quad-port 6Gb x8   <<<   Here I have a PCI Express 3.0 SAS RAID Card with write cache size upto 12GB

You could find more details about the SAS adapter assigned to your partition by referring to “SAS RAID Controllers” reference guide and searching for the “Customer Card ID Number” of your adapter, found using “lscfg -vpl sissas0” command.

 

 2 . Next, see the list of devices which are children of the SAS adapter ( and further SAS Protocol device ) :

# lsdev -p sissas0
sas0  Available 01-00-00 Controller SAS Protocol
sata0 Available 01-00-00 Controller SATA Protocol

# lsdev -p sas0
pdisk1   Available 01-00-00    Physical SAS Solid State Drive
pdisk2   Available 01-00-00    Physical SAS Solid State Drive
ses0     Available 01-00-00    SAS Enclosure Services Device
ses1     Available 01-00-00    SAS Enclosure Services Device

From the above output you could see that i have two Physical SAS Solid State Drives ( SSD ).
pdisks represent physical disks that are formatted to 528 bytes per sector. To be available for use by the AIX operating system or any application these pdisks should be part of a disk array and formatted to 512 bytes per sector.

 

 3 . For our work to configure the SAS disks we’ll use SMIT (easier than command, huh!). The ” smit sasdam ” fast path takes you directly to the main menu of “IBM SAS Disk Array Manager“.
To make a pdisk to be available for use in the SAS disk array select “Create an Array Candidate pdisk and Format to RAID block size“. Next, select the SAS controller “sisasas0” and press Enter.

Create_an_Array_Candidate_pdisk_and_Format_to_RIAD_block_size

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 4 . In the next screen select the disks from the list of pdisks assigned to the SAS adapter. Here i have selected both the available pdisks, pdisk1 and pdisk2.

Create an Array Candidate pdisk and Format to RAID block size -- Select pdisks

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 5 . On submitting the previous operation, the selected pdisks are formatted and the completion message is displayed once the operation is complete.

Create an Array Candidate pdisk and Format to RAID block size -- Format complete

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 6 . Now the pdisks are formatted and ready to be used for Disk Array. Next step is the create a disk array using these pdisks.
To get that done we need to return back to the main menu of “IBM SAS Disk Array Manager” in SMIT and select “Create a SAS Disk Array“.
Here again, we have to select the same SAS controller.

Create a SAS Disk Array

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 7 . The next step requires the desired “RAID Level” for the Disk Array to be selected.
You should select the appropriate RAID level based on your requirement. If not already familiar with use of RAID in data storage you could know more about it in this Wikipedia link : https://en.wikipedia.org/wiki/RAID. Here I have selected RAID 0 ( to get a single hdisk stripped across two physical disks i.e. pdisks ).
This means that the size of the created hdisk would be equal to the sum of both the pdisks. Also, stripping would help to improve the throughput achieved for the hdisk by distributing the read and write operations to both the pdisks in the order of the stripe size.

Create a SAS Disk Array- Select a RAID Level

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 8 . Next screen asks to select the “Stripe Size” to be used for striping.
Here I have selected the recommended value of 256Kb.

Create a SAS Disk Array-Select a Stripe Size

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 9 . Pdisks to be used in the disk array needs to be selected in the next screen. Here I have selected both the pdisks.
After the completion of this step a new hdisk would be created in my LPAR.

Create a SAS Disk Array - Select Disks to Use in the Array

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 10 . You could use this command to view the new SAS hdisk in your partition. For my case it was hdisk5 :

# lsdev -Cc disk | grep SAS
hdisk5 Available 01-00-00 SAS RAID 0 SSD Array


Voila, you have your SAS hdisk for use.

The disks that I had here were Solid State Drive(SSD) disks; and if you have SSDs in your machines, you could try out the dazzling and charismatic Flash caching feature in AIX which requires SSD disks.
You could not only increase the storage I/O throughput of your applications multifold; you would also reduce a lot of I/O congestion in your Storage Area Network(SAN).

A detailed article on the Flash caching feature of AIX is available in this IBM developer Works article : Integrated Server Based Caching of SAN Based Data.

Hope you found this article useful and please feel free to leave back any comments/suggestions you might have !

 

 

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