What Is a Parity Drive

What Is a Parity Drive

A parity drive is a storage device used as part of a computer system that contains parity data for redundancy and backup purposes. This is commonly part of a Redundant Array of Independent Disks (RAID), in which one or more disk drives are connected together to act as a single system. When data is stored on these devices, parity information can be created for use later in case one of the disks fails. A parity drive is not necessarily part of all RAID setups, but it allows for simple and effective data recovery.

The basic function of a parity drive is to provide additional storage of "parity bits," which are pieces of data used to backup the main drives in a disk array. An array is a computer setup in which multiple disks, such as two or more hard drives, are connected together and used as a single storage system. Although a number of different methods are used for this, a RAID is among the most common forms. There are various types of RAIDS, and more complex "levels" often include the use of a parity drive to provide effective backup and redundancy of information.

A parity drive functions through the use of parity bits that are stored on it. The simplest example of how parity bits function is in a RAID or other system that uses three drives in total. Two of the drives would be used as the actual data storage disks, while the third would function as a parity drive. Whenever data is saved to the RAID, each piece of information is split in half, with one part going onto one drive and the other part onto the second.

Computer data consists of bits, which are binary pieces of data represented by either a one or a zero. Whenever information is stored on a system with a parity drive, one bit from each storage drive is added to the other. If the result is an even number, then a parity bit with a value of zero is saved to the parity device, while an odd result creates a value of one. This can then be used if one of the storage drives fails, to recreate the data that is missing in order to restore what was lost.

For example, a "1" on one device, and a "0" on the other, would generate a "1" to be stored on the parity drive, since this is an odd value when added together. If the storage drive with the "0" data on it becomes corrupted, it can be replaced with a new, blank disk. The system can then look at the existing data, find the remaining "1" in data storage, compare that to the "1" in the parity device, and recognize that a "0" needs to be recreated to restore the lost data. This is redundancy and allows an array to effectively recover data even if part of the original system is lost.

Click here for related posts...

Storage Technology EMC CLARiiON SAN array

Netapp Basic Setup Wizard

First things first, before getting started you need to create yourself a login at the Netapp NOW website http://now.netapp.com It usally takes 24-48 hours for your login to become active. The NOW website is where you get access to all the documentation, knowledge base, articles, software, licenses, etc

Once you’ve racked and cabled your Netapp SAN, according to the documentation on your SAN model you’re ready to start configuring.

Connect the supplied console cable to your pc and start your favourite terminal emulation program. I mainly use Putty which can be downloaded from here http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html

As you power on the SAN it will go through all the POST tests and finally arrive at the setup wizard prompt

1. Enter the new hostname (Tip: When Netapp support refer to your controllers, they refer to them as top or bottom. To make it simple try and name and controller at the top something ending in top and for the bottom, something ending in bot. You don’t need to do this but it is less confusing later on down the track)

2a. Do you want to configure interface groups ? (On the back of our FAS2040 we have 4 gigethernet ports named e0a, e0b, e0c, e0d. You have the option of bundling 2 or more of these to create an etherchannel to your switch. This becomes beneficial if you are considering running iscsi, nfs or cifs as the traffic can be load balanced across the bundled ports. Within an interface group you can also create vlans to segment traffic, however I’ll touch on this a little later on. You don’t need to create an interface group, you can answer no here and configure a single port)

How to Verify if the Cache Batteries are Good in a StorageWorks Modular Storage Array (MSA) 20

When one or both of the batteriesin an HP StorageWorks Modular Storage Array (MSA) 20 Controller are failed,disconnected, or not seated properly, the MSA20 does not run in an optimalmode. Write cache is disabled if a battery is failed, not present, or seatedimproperly. As a result, the MSA20 could have significant loss of sequentialwrite performance. Each MSA has the 7-segment display and the status messagepertains to the two batteries attached to that MSA only. Each MSA in yourenvironment should be checked for this issue.

MSA20s running Firmware v2.00 orlater in any configuration

Use the following checklist toverify this condition for MSA20s running firmware v2.00 or later.

NOTE: This applies to both MSA20s attached directly to a SmartArray controller and to MSA20s attached behind an MSA1500cs or MSA1510i.

1.    For battery failure status, the 7-segment display on the rear ofthe MSA20 displays the following:

a.    F1 indicates lower battery packfailure (MSA Battery #1 - attached directly to cache).

b.   F2 indicates upper battery packfailure (MSA Battery #2).

c.    F3 indicates both types of batterypack failures.

SAN Interview questions

SAN Interview questions

1. WHAT ARETHE BENEFITS OF FIBRE CHANNEL SANS?

 Fibre Channel SANs are the defacto standard for storage networking in the corporate data center because theyprovide exceptional reliability, scalability, consolidation, and performance.Fibre Channel SANs provide significant advantages over direct-attached storagethrough improved storage utilization, higher data availability, reducedmanagement costs, and highly scalable capacity and performance.

2. WHAT ENVIRONMENT IS MOST SUITABLE FOR FIBRECHANNEL SANS?

Typically, Fibre Channel SANs are most suitable for large data centers runningbusiness-critical data, as well as applications that require high-bandwidthperformance such as medical imaging, streaming media, and large databases.Fibre Channel SAN solutions can easily scale to meet the most demandingperformance and availability requirements.

3. WHAT CUSTOMER PROBLEMS DO FIBRE CHANNEL SANSSOLVE?

The increased performance of Fibre Channel enables a highly effective backupand recovery approach, including LAN-free and server-free backup models. Theresult is a faster, more scalable, and more reliable backup and recoverysolution. By providing flexible connectivity options and resource sharing,Fibre Channel SANs also greatly reduce the number of physical devices anddisparate systems that must be purchased and managed, which can dramaticallylower capital expenditures. Heterogeneous SAN management provides a singlepoint of control for all devices on the SAN, lowering costs and freeingpersonnel to do other tasks.

4. HOW LONG HAS FIBRE CHANNEL BEEN AROUND?

Development started in 1988, ANSI standard approval occurred in 1994, and largedeployments began in 1998. Fibre Channel is a mature, safe, and widely deployedsolution for high-speed (1 GB, 2 GB, 4 GB) communications and is the foundationfor the majority of SAN installations throughout the world.

5. WHAT IS THE FUTURE OF FIBRE CHANNEL SANS?