MrBenchmark

Monday April 04, 2005

RAID-1 vs RAID-5 on Solaris 10 - Part 1/7

Well, today went so fast I had no chance to write an entry in MrBenchmark's blog.

Sorry to disappoint you but I will not talk about the best winery of the Napa valley or the movies I saw last week. Instead, I'd like to start today a serie of blog entries on the topic of RAID-1 vs RAID-5 on Solaris 10.

I will start today by an Introduction and some Concepts

1. Introduction

We are regularly engaged by Fortune 500 companies to assist in determination of the right IO subsystem for their future information systems. The task of choosing the appropriate IO subsystem must take into considerations many factors like availability, capacity, performance, heterogeneity or price. Capacity and performance are both the consequences of one major decision : the RAID level.

The main goal of this study is to compare RAID-1 and RAID-5 performance on three important IO subsystems out of the Sun Microsystems available products : the SE6120, SE3510 and SE9980. RAID-0 configurations are not part of this study as they are rarely requested by our customers and not available on the SE9980.

Please find below the definition of what we freely refer in this document as RAID-1 and RAID-5 :

• RAID-1 is implemented on modern IO subsystems as hardware RAID-1+0.It allows mirroring and disk striping in one step. The total usable capacity is the capacity of half the drives used to create the Logical Unit (or Lun).
• RAID-5 implements multi-block striping with distributed parity. This RAID level offers redundancy with the parity information distributed across all disks in the array. Data and its parity are never stored on the same disk. In the event that a disk fails, original data can be reconstructed using the parity information and the information on the remaining disks.

By stating this, we realize easily that performing this comparison apples-to-apples is a difficult task. If we use the storage architect point of view, we would compare this two layout technics by capacity . It basically means to compare the performance of a RAID-1 (3+3) lun to a RAID-5 (3+1) lun. From the system engineer point of view, the problematic is more to help the customer configure a storage subsystem that has been purchased to the best of the business requirements interests. As an example, if the customer purchased a SE3510 FC array with two RAID controllers, how should this IO subsystem be configured to ensure good performance, low cost per gigabyte and good reliability (in the customer order) ?

We have chosen the second approach, by spindles, as this is the most common question issued by the sales force. It means that a RAID-1 (3+3) lun will be compared to a RAID-5 (5+1) lun. We will not answer directly to the configuration question, but we hope we will provide you the data to answer it case-by-case in confidence.