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Direct Attached Storage (DAS)Direct Attached Storage (DAS)

Module 3.1

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Direct Attached Storage (DAS)

After completing this module you will be able to:

Discuss the benefits of DAS based storage strategy

Describe the elements of DAS

Describe the connectivity options for DAS

Discuss DAS management considerations

Identify the best environments for DAS solutions

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What is DAS?

Internal External Direct Connect

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DAS Benefits

Ideal for local data provisioning

Quick deployment for small environments

Simple to deploy in simple configurations

Reliability

Low capital expense

Low complexity

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Physical Elements of DAS

CPU

Motherboard

Clustered group of processors

Processor cards

Complete system

Internal

External

Hard disk(s)

CD-ROM drive

Optical drive

Removable media

Tape devices/tape library

RAID/intelligent array(s)

Portable media drives

Connectivity

Storage

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DAS Connectivity

Block-Level Access Protocols:

ATA (IDE) and SATA– Primarily for internal bus

SCSI– Parallel (primarily for internal bus)– Serial (external bus)

Buss and Tag – Primarily for external mainframe– Precursor to ESCON and FICON

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DAS Connectivity: Internal

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Internal DAS Connectivity Examples

Parallel Connectivity Cables

34-wire floppy cable

80-wire IDE cable

50-wire SCSI-2 cable

Serial ATA cable

Serial Connectivity Cable

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DAS Connectivity: External

Host Storage Device

External DAS

HBAHBA

Example of an external connectivity cable

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DAS Management: Internal

Host provides:– Disk partitioning (Volume management)

– File system layout

– Data addressing

Direct Attached Storage managed individually through the server and the OS

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DAS Management: External

Array based management

Availability – multi-path I/O

Lower TCO for managing data and storage Infrastructure

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DAS Performance Considerations

Factors to be considered for DAS performance:

• Hard disks

• Memory cache

• Virtual memory (paging)

• Storage controllers• Protocol supported (e.g. SCSI, FireWire, USB, etc.)

• RAID level

• Bus

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Internal DAS Application Example

Hard Drive

40 Pin Ribbon Cable

Motherboard

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External DAS Application Example

ESCON HBACable for

external DAS connectivity

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DAS Challenges

Hosts must be directly connected

Data availability

Data slowdowns possible– CPU congestion, caching, multi-pathing

Scalability is limited– Number of connectivity ports to hosts

– Number of addressable disks

– Distance limitations

Downtime required for maintenance

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Module Summary

Key points covered in this module:

DAS can be:– An integrated part of the host computer

– Directly connected to a single server

DAS is made up of a CPU, connectivity, and storage devices – There are several options within each of these categories

DAS connectivity uses block-level access protocols

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Check Your Knowledge

What are the physical elements of DAS?

Give an example of when DAS is a good solution.

Describe internal DAS connectivity.

Describe external DAS connectivity.

What are some areas that you need to consider as part of DAS management?