Generic Storage System Architecture

The above diagram shows a generic stand-alone storage system architecture, where a storage OS is installed over a bare metal server and thus making it a storage server. Here I am using an enterprise class storage OS named Open-E DSS V7 which is installed on a Dell PowerEdge R720xd. R720xd can have up to twelve 3.5" drives at the front plus two 2.5" drives at the rear. Here in the diagram, the last 2 disks (Disk Group03) are 2.5" drives installed at the rear and being used as OS drive in RAID1. Apart from that we have five SAS 7.2K and 15K disks that are grouped into two RAID groups. Comparing the disk IOPS 'Disk Group01' can be considered fast and 'Disk Group02' as slow.

As I haven't mentioned the size of each SAS disk, lets assume using 'Disk Group01' a 10TB RAID5 virtual disk (VD) is created and using 'Disk Group02' a 12TB RAID5 VD is created. You can configure hot spares for each disk group if you have additional disks. As I mentioned above, for OS installation we have created a 10GB RAID1 VD using 'Disk Group03'. After installation of the OS (Open-E DSS V7), it scans and shows 10TB and 12TB as available storage units. 

Now the next step is to create volume groups. Here we created two volume groups (VG00 and VG01) to differentiate fast and slow storage. 

• VG00 uses VD01
• VG01 uses VD02

Once volume groups are created, you can now carve out LUNs separately based on your requirements. For example, if you want a LUN that is going to be used as a datastore to store your virtual machines, then you can create it on VG00 (fast), or if you need it for storing some general purpose backup files, then you can create it on VG01 (slow). So depending on your requirement you can decide where to create your LUN.

Note: Here I classified RAID disk groups based on speed. You can divide it based on reads and writes. So that you can choose RAID10 disk group for write intensive operations and RAID5 disk group for reads. It can even be divided based on access type. That means a disk group exclusively for sequential file access (SQL logs) and another disk group for random access (SQL data, VM datastore etc). 

Best practices while virtualizing Microsoft SQL servers using Hyper-V

-Limit min and max memory for SQL server
-Use fixed size VHDX
-Split data and log files into separate VHDX disks
-Use multiple SCSI controllers
-Right sizing and not over allocating resources
-Making use of multiple RAID disk groups (for sequential and random access)
-For tier-1 mission critical applications use RAID 10 for data, log files, and tempDB for best performance and availability
-For lower tier SQL workloads when cost is a concern, data and tempDB can be on RAID 5
-Use of SSDs or tiered storage for higher IOPS
-If using VMQ on Hyper-V environment, on the guest OS side you can enable vRSS for processing network load across multiple CPUs
-I prefer using fixed size memory for SQL VMs
-Exclude SQL DB related files  from (*.mdf, *.ldf, *.ndf, *.bak, *.trn) on access antivirus scan
-Disable content indexing on SQL data/ log/ tempDB drives
-Enable lock pages in memory (group policy setting)
-DB IFI (Instant File Initialization)
-Set OS power plan to high performance
-OS performance options - visual effects - adjust for best performance

RAID configuration using PERC

PERC stands for PowerEdge Raid Controller. Here we have 3 physical disks present. We will be configuring 2 virtual disks (VD) of RAID 5 using these 3 physical disks.

VD00 - 100 GB

VD01 - 1.7 TB

Once the system starts press Ctrl+R to enter PERC configuration utility and follow the steps as shown below.

No configuration present and 3 disks available

Press F2 and create new VD

VD00 properties

Click OK

VD00 - 100 GB created

Press F2 and add new VD

VD01 properties

VD00 and VD01 created

 Now we have successfully created 2 VDs. Next step is to initialize both VDs.

Initialization of VD00

Start Init

Click OK

Initialization VD00 in progress

Similarly initialize the next VD too. Once its completed you can exit from the PERC utility and reboot the machine.

RAID controller

As RAID controller is responsible for the operations on RAID array drives, it is very important to have an enterprise class controller for enhanced performance, increased reliability and fault tolerance. Considering the business requirement and budget, you can choose a RAID controller. Here I will be explaining about DELL Power Edge RAID Controller (PERC). When choosing a controller, there are few critical hardware features that affect performance to keep in mind :

• Read policy
• Write policy
• Controller cache memory
• CacheCade
• Cut-through I/ O
• FastPath

PERC Series

PERC H810 - high performance RAID controller that can be connected to JBOD

PERC H710P - ideal for implementing hybrid server platforms based on SAS HDDs with high performance and enterprise class reliability

PERC H310 - entry-level RAID controller (no cache)

Reference :
Dell
Microsoft

How to calculate total IOPS supported by a disk array

IOPS stands for input/ output operations per second. 

Consider a RAID array with 4 disks in RAID 5. Each disk is 4TB 15K SAS drive. We can use the below formula for calculating maximum IOPS supported by the RAID array.

Raw IOPS = Disk Speed IOPS * Number of disks

Functional IOPS = (Raw IOPS * Write % / RAID Penalty) + (RAW IOPS * Read %)

No: of disks = 4 (4TB 15K SAS)

IOPS of a single 15K SAS disk = 175 - 210

RAID penalty = 4 (for RAID 5)

Read - Write ratio = 2:1 (say we have 66 % reads and 33 % writes)

From the above details :

Raw IOPS = 175 * 4 = 700

Functional IOPS = (700 * 0.33 / 4) + (700 * 0.66) = 519.75

Therefore, the maximum IOPS supported by this RAID array  = 520

The above calculation is entirely based on assumption that the read - write ration is 2:1. In real time scenarios it may vary depending on the type of workload. That means workload characterization is also important while calculating maximum IOPS value supported by your RAID array. It also depends on the type of RAID, as penalty will be different for different type of RAID. Disk type (SSD, SAS, SATA etc), disk RPM and number of disks also affects the total IOPS value.

From this we can conclude that, if your current IOPS usage is closer to the maximum IOPS supported, then you have to be very cautious as it may lead to I/O contentions due to heavy workloads causing high latency and performance degradation to your storage server.

RAID

RAID stands for Redundant Array of Inexpensive/ Independent Disks. There are different RAID levels and the level you choose for your system depends on the amount of storage you require and the way you access your data and several other factors like cost, redundancy etc. Common RAID levels are 0, 1 and 5.

RAID 0

-Data stripping

-Improved performance

-No redundancy

RAID 1

-Mirroring

-Redundant

RAID 5

-Data stripping + evenly distributed parity

-Redundancy + improved performance

-Minimum 3 hard disks required

RAID is mostly used in a production setup or where redundancy and performance is a major concern. It is configured by using RAID controllers. For example, in the case of Dell PowerEdge R710 servers, RAID is configured using PERC (PowerEdge Raid Controller). Press Ctrl+R to access the PERC BIOS Configuration Utility after starting or restarting the PowerEdge server.