This document discusses direct-attached storage (DAS), which connects storage devices directly to servers. It describes the internal and external DAS architectures, with internal DAS having the storage device inside the host and external DAS connecting the storage device externally via interfaces like SCSI. DAS has benefits like lower cost and simpler setup than networked storage but lacks scalability and can be limited by bus bandwidth and distance restrictions. Performance depends on factors like disk utilization, cache memory, RAID configuration, and controller protocols.

2.  Disk Drive Components, Disk Drive
Performance, Host Access to Data, Direct-
Attached Storage , Storage Design Based on
Application Requirements and Disk
Performance, Disk Native Command Queuing,
Introduction to Flash Drives.
 Concept in Practice: VMware ESXi.
Storage System Environment - 2

3. Storage System Environment - 3
Interface
Controller
Power
Connector
HDA

4. Physical Disks - 4
00110100111010101010
00110100111010101010
10110101011010101010
01010100111010101010

5. Physical Disks - 5
Spindle
Platters

6. Physical Disks - 6

7. Physical Disks - 7
Actuator
Spindle

8. Physical Disks - 8
Actuator
R/W Head
R/W Head

9. Physical Disks - 9
Bottom View of Disk Drive
HDA
Controller
Interface
Power
Connector

10. Physical Disks
-
10
Sector
Track
Platter

11. Physical Disks
Platter Without Zones
Sector
Track
Platter With Zones

12. Physical Disks
-
12
Cylinder
Tracks, Cylinders and Sectors

13. Physical Disks
Physical Address = CHS Logical Block Address = Block #
Sector
Cylinder
Head
Block 0
Block 16
Block 32
Block 48
Block 8
(lower surface)

14. Physical Disks
-
14
A
Concatenation -
One Logical Volume
Partitioning -
Multiple Logical Volumes
A
B
C
D

15.  Seek time is the time for
read/write heads to move
between tracks
 Seek time specifications
include:
◦ Full stroke
◦ Average
◦ Track-to-track
Physical Disks
-
15

16.  Direct – Attached storage (DAS) is a an
architecture where storage connects directly
to servers.
 Applications access data from DAS using
block-level access protocols.
 DAS is ideal for localized data access and
sharing in environments that have a small
number of servers.
 Ex: small businesses, departments and
workgroups do not share information across
enterprises

17.  There are two types of DAS depending on the
location of the storage device with respect to
the host.
 Internal DAS
 External DAS

18.  In the internal DAS architecture, the storage
device is internally connected to the host by a
serial or parallel bus.
 The physical bus has distance limitations and
can only be sustained over a shorter distance
for high-speed connectivity.
 Most internal buses can support only a
limited number of devices
 They occupy a large amount of space inside
the host, making maintenance of other
components difficult

19.  In the external DAS
architecture, the
server connects
directly to the
external storage
device.
 Communication
between the host
and the storage
device takes place
over SCSI (Simple
Computer System

20.  DAS needs lower initial investment than
storage networking.
 It is simple and can be deployed easily and
rapidly.
 Setup is managed using host-based tools like
host OS.
 It requires fewer management tasks and less
hardware and software elements to set up
and operate.
 But it is not scalable.

21.  A storage device has a limited number of
ports.
 A limited bandwidth in DAS restricts the
available I/O processing capability.
 The distance limitations associated with
implementing DAS because of direct
connectivity requirements can be addressed
by using Fibre Channel connectivity.
 Unused resources cannot be easily re-
allocated, resulting in islands of over-utilized
and under-utilized storage pools.

22.  Disk utilization, throughput, and cache
memory of a storage device, along with
virtual memory of a host govern the
performance of DAS.
 RAID-level configurations, storage controller
protocols, and the efficiency of the bus are
additional factors that affect the performance
of DAS.
 The absence of storage interconnects and
network latency provide DAS with the
potential to outperform other storage
networking configurations.