This post was written by Phani MV, Engineer in Global Solutions Engineering.

Are you a storage architect/solution designer/are you considering or designing SAN solution for your IT infrastructure? Then at some point in time you might have come across same the question – which I had “How do I size my storage”?

This question is particularly important for Dell Compellent because sizing greatly depends on storage architecture. In this post I tried to address the question.

Dell Compellent automated tiered storage is based on fluid architecture- means data cannot be static, it moves dynamically. The core strengths of Compellent Storage center are Dynamic block architecture, Intelligent Tiering, Data Progression. Virtualization at disk level helps Compellent automatically creates tiers from the hard drives presented to the storage center.

Once you load the drives in storage enclosures Compellent software technology takes care from there on, right at this moment million dollar questions arise.

• How many tiers do I need for my configuration?
• What type of drives do I need? (SSD, SAS 15K, SAS 10K and many more).
• How many numbers of drives do I need in each tier?
• What type of RAID should I use/suggest?
• How many storage enclosures do I need?

and the questionnaire goes on.

SAN sizing varies from case to case. Though there is no standard method to size a SAN for Oracle deployment, I have some guidelines for you.

Let’s understand it with an example:

In a typical Oracle deployment say requirements are as below:

Usable Capacity required = 10 TB

IOPS required = 3000

Read: Write mix = 50:50

Based on Dell Compellent recommendation I have the below golden rules:

• Tier 1 should be configured to deliver the required IOPS
• Tier 2/Tier3 should be configured to deliver the capacity requirements.

Below table gives you a snapshot of how Compellent tiers the drives.

NOTE: The above table shows only 3 combinations but not limited to only 3, based on different drives and combinations available user can have different tiers.

Click here for more information on Compellent Tiering.

Table below gives snapshot of rough estimate of IOPS per different drive.

Keeping above points in mind let’s start finding the numbers:

My assumptions / consideration:

Tier 1 configuration:

IOPS required = 3000 
Based on read: write mix 50:50:- Read IOPS = 50% of 3000 = 1500,
write IOPS = 50% of 3000 = 1500
Considering raid 10 write penalty (click here for more information on raid penalties).
Total write IOPS = 2 * 1500
Total backend storage IOPS = 1500 + 2 * 1500 = 4500
Number of drives required for Tier 1 = 4500/180 = 25
Hot spares = 2
Total Tier 1 drives = 27
Capacity contribution from tier 1 drives = ~2.3TB

Tier 3 configuration:

Usable Capacity requirement = 10TB
Replay over head = 20%
Total capacity required = Usable + replay overhead = 10TB + 20% of 10TB = 12TB
Raid 6 over head = 0.8
Tier3 required = Total capacity required – Capacity contribution from Tier1
= (12 – 2.3)/0.8 = ~13TB
Drives required = 13/931GB (for 1TB drives usable space = 931GB) = 15
Hot spares = 2
Total tier3 drives = 17

For more information visit Dell Compellent storage. Visit Dell Oracle solutions for latest database solutions release.

If you have any feedback or questions reach out to me @ Phani_mv@dell.com