STK12C68-C25I [SIMTEK]

Non-Volatile SRAM, 8KX8, 25ns, CMOS, CDIP28, 0.300 INCH, CERAMIC, DIP-28;


型号：	STK12C68-C25I
厂家：	SIMTEK CORPORATION
描述：	Non-Volatile SRAM, 8KX8, 25ns, CMOS, CDIP28, 0.300 INCH, CERAMIC, DIP-28 可编程只读存储器电动程控只读存储器电可擦编程只读存储器 CD 静态存储器内存集成电路
文件：	总4页 (文件大小：36K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

Using nvSRAM in RAID

Controller Applications

evens out the number of I/O requests per disk and

greatly speeds up the disk access. The trouble with

disk tuning is that it requires a lot of system adminis-

tration time to accomplish, and when done, there is

no guarantee that it will stay balanced. In a dynamic

system the I/O load will change with time and there-

fore will require constant tweaking to maintain peak

efficiency. A better solution is to use an array of

disks. The RAB defines an array of disks as “a col-

lection of disks from one or more commonly acces-

sible disk subsystems, combined with a body of

Array Management Software (AMS)”.

Introduction

The term RAID (Redundant Array of Independent

Disks) first appeared in papers written by Garth Gib-

son, Randy Katz, and Dave Patterson of the Univer-

sity of California at Berkeley. Since that time the

number of manufacturers of RAID systems has

expanded to over 100 companies with product lines

that range from high end commercial products to

lower cost controllers for the home market.

The RAID advisory board (RAB) was formed in 1992

to help minimize confusion within the industry by

standardizing terminology and maintaining stan-

dards for the classification and typing of controllers.

The board is comprised of over 40 members and

continues to promote the industry by encouraging

the development of hardware components that are

optimized for RAID applications. The goal of the

RAB is to become a compliance verification and

testing organization that will issue product approv-

als, act as a regulatory agency, and assure users

that the RAID level claimed by the manufacturer

meets RAB standards. The RAB also will perform

testing to certify that vendor hardware meets RAB

requirements for Array-Ready Disks, and verify Disk

Array Performance Benchmarks.

Array Management Software is usually defined as

firmware that executes in a dedicated control sys-

tem rather than the host computer and has two

major functions. Function one is to map the storage

space available and optimize system balance to

maximize disk I/O performance. Function two is to

present storage to the operating environment as vir-

tual disks by converting I/O requests to virtual disk I/

O requests. This gives the appearance of a single

large disk to the system and frees the administrator

from constantly having to tweak the data distribu-

tion. Disk arrays generally have improved I/O perfor-

mance, and simpler storage management

requirements than a string of parallel disks.

RAID Theory Overview

The next task facing the designer of RAID systems

is to assure that data stored in the array can never

be lost due to hardware failure. Major users of disk

array systems such as banks, airlines, and credit

agencies must be certain that they can never lose a

disk in such a manner that the data stored on that

disk is not recoverable. Even frequent and consci-

entious backing up of all disk storage does not

recover new data that has been written since the

last backup cycle was performed. A solution to this

data reliability problem is the use of a RAID Control-

ler. RAID Controllers are defined with 7 levels:

For disk I/O intensive systems there are two charac-

teristics that act as the primary system performance

bottlenecks:

1. Data Seek Time

2. I/O Transfer Rates

It would seem logical that all that is required to

reduce the time necessary for the computer to fetch

data from the disk is to use multiple disks in parallel

and distribute the data. While this solution sounds

easy and cheap, the realities of life aren’t so simple.

As any experienced system administrator can tell

you 80% of the total I/O load of a system is directed

at 20% of the I/O resources. This so-called 80/20

rule requires that the I/O system be tuned to distrib-

ute the load over the bank of parallel disks. This

Level 0 - Data Striping

Level 1 - Disk Mirroring

Level 2 - Hamming Code

Level 3 - Parallel Transfer Disks with Parity

8-25

Using nvSRAM in RAID Controller Applications

Level 4 - Independent Access Array

Level 5 - Independent Access Array with Rotating . .

Parity

RAID Level 3

RAID 3 is optimized for high data transfer rates and

is a parallel transfer technique with parity. Each data

sector is subdivided, and data is scattered across all

data disks with redundant data being stored on a

dedicated parity disk. Reliability is much higher than

a single disk and the data transfer capacity is the

highest of all listed RAID types. RAID 3’s weakness

lies in its relatively slow I/O rates that make it unsuit-

able for most transaction processing unless assisted

by some other technology such as cache. The parity

disk stores redundant information about the data

chunks stored in corresponding locations on the

data disks. The redundant information is typically in

the form of a bit-by-bit Exclusive OR function of cor-

responding data chunks from the other disks. Typi-

cal applications for RAID 3 include large data

objects such as CAD files, graphical images, seis-

mic or telemetered data streams.

Level 6 - Recovery from the failure of up to 2 disks

RAID Level 0

A stripe set presents a single virtual disk whose

capacity is equal to the sum of the capacities of its

members. The reliability of the stripe is less than the

reliability of its least reliable member and its read

and write rates are high. RAID 0 is not a true RAID

controller because it provides no redundancy. It is,

however, a performance-oriented architecture that is

inexpensive and therefore attractive to many low

cost users. RAID 0 is a parallel transfer technology.

RAID Level 1

A mirror set also presents a single virtual disk; its

capacity however is equal to that of its smallest

member. Its reliability is very high, its read perfor-

mance is usually better than that of a single mem-

ber, but its write performance is somewhat slower. A

RAID 1 system protects against disk failure by repli-

cating all stored data at least once on a physically

separate disk. RAID 1 can be implemented as either

a parallel or independent array and is well suited to

applications that are read intensive and where reli-

ability requirements are high.

RAID Level 4

RAID level 4 is an independent access array in

which data sectors are distributed in a similar man-

ner to disk striping systems. Redundant data is

stored on an independent parity disk (similar to

RAID 3). Its data reliability is much higher than a sin-

gle disk (comparable to RAID 2, 3, and 5) and its

data transfer capacity is moderate. RAID 4 is a high

I/O read rate technology with moderate write

speeds, but is not well suited for high data transfer

applications due to the parity disk write bottleneck

Two of the four operations required to perform a vir-

tual disk write are directed at the parity disk; for this

reason RAID 4 arrays are seldom implemented.

Possible applications would include systems that

are read intensive and do not require high data

transfer rates.

RAID Level 2

A parallel access array that uses Hamming Coding

to provide error detection and correction capability

to the array. This approach is very expensive and

therefore almost never implemented into a system.

Virtual Disk

RAID Level 5

RAID level 5 is an independent access array with

rotating parity. Data sectors are distributed in the

same manner as disk striping systems but redun-

dant information is interspersed with user data

across multiple array members rather than stored

on a single parity disk as in RAID 3/4 systems. This

relieves the write bottleneck associated with RAID

level 4 controllers. RAID 5 arrays have high data

reliability, good data transfer rates and high I/O rate

capability. It is well suited to applications such as on-

line customer services, inquiry-type transaction pro-

cessing, group office automation, etc.

Array Management Software

Data Disk

Parity Disk

Figure 2

Example of a Typical RAID Level 3 or 4 Controller

From The Roadblock Edition 1-1

8-26

Using nvSRAM in RAID Controller Applications

as airline reservation systems, financial and banking

applications, etc.

RAID Level 6

RAID 6 is a non-Berkeley level controller that is

designed for extremely high data reliability. RAID 6

is an independent access array concept that

requires two parity blocks be updated for each block

written. This requires an extra parity disk but gives

nvSRAM Applications & System Archi-

tecture

In modern RAID systems the Array Management

Software can run in the host or in a dedicated

embedded controller. Most modern systems are

using embedded controllers, including many manu-

facturers using the Intel i960 chip as the engine.

the added data safety of requiring 3 disks to fail

before data will be lost. RAID 6 data transfer and I/O

capability is lower than RAID 5 for writes, but data

reliability is highest of all RAID architectures. Pres-

ently RAID level 6 is not widely used because of the

higher costs associated with the added complexity,

and the high penalty paid in system I/O performance

due to long write times.

In the past RAID systems were designed to use a

distributed block of disk to maintain system configu-

ration and to store system recovery address vec-

tors. The primary problem with this type of

architecture is that if a power failure occurs, and the

controller’s volatile system memory is lost, the entire

disk array must be scanned upon power up to rees-

tablish configuration and to redefine data locations.

On a large array this is very time consuming, requir-

ing many minutes to accomplish. Service-oriented

industries cannot afford this length of down time and

must come up and be operating very quickly once

power is restored. In the latest generation of RAID

systems the restart vectors are stored in nonvolatile

semiconductor memory on the controller board

itself. Due to the fact that the Array Management

System is constantly moving data among the indi-

vidual array members to optimize I/O balance, maxi-

mize I/O rates, and assure redundancy, the RAID

controller is constantly tweaking the address vector

tables. Also, the system configuration data is being

Additional RAID Implementations

RAID 10 is a combination of RAID 0 & 1. This archi-

tecture gives high I/O performance and good data

reliability. It is accomplished by using RAID 0 (data

striping) to enhance I/O rates and by using RAID 1

(disk mirroring) for high data reliability. RAID 10

requires costly hardware (disk and port) to imple-

ment, and is primarily used in applications where the

data has high value and can justify a mirrored stor-

age system.

RAID 53 is a combination of RAID levels 0 & 3 and

provides RAID 3-like data transfer performance, and

striping-like I/O request rates at RAID 3 or 5 costs.

RAID 53 is used where both high data request rates

and high data transfer performance is required such

Physical

Disk 0

Physical

Disk 1

Virtual

Disk

Chunk 0

Chunk 4

Chunk 8

Chunk 12

Chunk 1

Chunk 5

Chunk 9

P (12-15)

Physical

Disk 2

Chunk 0

Chunk 1

Chunk 2

Chunk 3

Chunk 4

Chunk 2

Chunk 6

P (8-11)

Chunk 13

Chunk 5

Array

Management

Software

Chunk 6

Physical

Disk 3

Chunk 7

Chunk 8

Chunk 9

Chunk 10

Chunk 11

Physical

Disk 4

Chunk 3

P (4-7)

P (0-3)

Chunk 7

Chunk 11

Chunk 10

Chunk 14

Chunk 15

Figure 2

Example of a Typical RAID Level 5 Controller

From The RAID Book Edition 1-1

8-27

Using nvSRAM in RAID Controller Applications

stored simultaneously in several different locations,

and parity information is being maintained to allow

recovery in case of disk failure. This constant mov-

ing of data and reconfiguring of the array, requires

that the configuration address vectors be stored in a

nonvolatile technology that is rapidly rewritable. This

memory must be fast enough to run at processor

bus speeds so the RAID controller does not have to

waste time blindly searching the disk array for its

configuration data.

rity of a less dynamic technology. This part has high

applicability to RAID controllers for address vector

and configuration storage.

The STK12C68/STK14C88 Family

The SIMTEK STK12C68/STK14C88 AutoStore™

family combines the flexibility of the 10Cxx family,

the data security of the 11Cxx family, and adds the

capability to perform power down AutoStore™ to

assure that data is never lost.

The SIMTEK family of nonvolatile SRAM products

are ideally suited to RAID applications. They run at

processor speeds, require no batteries for nonvola-

tility, are standard size and shape for automatic

manufacturing, and are flow solderable. The high

number of nonvolatile stores (1 Million), fast read

and write times (20 ns), and fast store times (10 ms)

allows the design of highly efficient embedded con-

trollers for both commercial and home applications.

The 12C68/14C88 family uses the same STORE

and RECALL techniques that are used with the

10Cxx and 11Cxx parts, but also gives the design

engineer the flexibility of automatically storing on

power down. AutoStores™ are autonomously per-

formed (unless inhibited) when system power falls

below V_SWITCH(about 4.25 V). This assures that

data is always safe and requires no batteries or

other power sources that are prone to failure. RAID

controllers that are dynamically keeping track of

address vectors, system configuration, and disk

error recovery information are ideal applications for

this family of parts.

Applying SIMTEK nvSRAM To Modern

RAID Controllers

The STK10Cxx Family

Conclusion

The SIMTEK STK10Cxx family of nvSRAMs is a

high performance nonvolatile memory family that is

designed for easy interface to embedded control-

lers. The STK10Cxx family is designed for dynamic

applications that require easy transfer from SRAM

to nonvolatile memory under processor control.

Using the 10Cxx family for store and recall of

address vectors, configuration databases, and error

detection/correction codes is an ideal application.

Modern RAID Controllers offer high data reliability

and increased I/O performance in one package.

This requires that the RAID system designer utilize

the latest in high performance embedded proces-

sors, state-of-the-art software, and sophisticated

control algorithms.

The flexibility of fast nonvolatile memory for the stor-

age of RAID address vectors, system configuration

information, and adaptive algorithm memory is

becoming more apparent with each new generation

of system. SIMTEK’s family of fast nvSRAMs are

ideally suited to this type of high performance appli-

cation. They run at processor speeds with no wait

states, reliably store data in a nonvolatile semicon-

ductor memory without batteries, and look to the

processor like a standard SRAM. Ease of imple-

mentation and ability to rapidly change data, as well

as the ability to use modern manufacturing tech-

niques, helps to reduce costs and to speed product

to market.

Data within the SRAM is stored to nonvolatile mem-

ory by simply requesting an SRAM write with the NE

line active. This transfers data from the SRAM to

shadow EEPROM in 10 ms. Data in the EEPROM is

then completely nonvolatile and requires no batter-

ies, capacitors or other energy sources to remain

stored for 10 years.

The STK11Cxx Family

The SIMTEK STK11Cxx family of nvSRAMs is

designed for use in applications where data must be

safely maintained in a fast nonvolatile memory, but

does not require the dynamic store capability of the

STK10Cxx family.

The STK11Cxx family of parts uses a software store

and recall system that allows the flexibility of a fast

nonvolatile SRAM memory, but offers the data secu-

8-28

STK12C68-C25I [SIMTEK]

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