几种Nand flash文件系统的对比

几种

Nand flas

文件系统的对比

1.

来源：

NLE-FFS: A Flash File System with PRAM for

Non- linear Editing

For thesedevices, NAND flash memory has became the most

attractive storage medium due to outstanding characteristics

such as its increased capacity, low power consumption, small

size and light weight. For the efficient management of NAND

flashmemory, several flash file systems have been proposed,

including

JFFS2, YAFFS2, CFFS and PFFS

. several file systems

such as

MNFS,NAMU and ScaleFFS

have been designed for

real-time recording /playback and large-capacity storage.

A. YAFFS2

YAFFS2 is the most widely employed file system for

NAND flash memory. YAFFS2 essentially saves the object ID

(file

ID) and the

chunk

(page)

number

in the

spare region to

show the offset of a page and the owner file of the page.

Therefore, YAFFS2 reads the spare regions and object

headers to establish the metadata in memory.

Although YAFFS2 is designed to support NAND flash

memory, it has scalability problems. With YAFFS2, the

location

of

the

updated

page is saved

in NAND

flash

pages

or

spare

regions,

as

shown

in

Fig.

10

(a);

hence,

the

file

system

should scan the entire flash space at the mounting time.

Moreover, the entire directory and file system structures

must be saved in main memory at that time. Thus, the mounting

time and the memory usage are increased linearly according to

the

NAND

flash

size

and

the

number

of

2

has

another

problem in which many pages are consumed during metadata

updates. The metadata are frequently updated and most of the

metadata updates are performed in several bytes. Metadata

updating

creates

large

numbers

of

invalid

pages.

This

severely

degrades the write performance due to garbage collection, as

byte-level

updates

and

in- place

updates

are

not

allowed

in

NAND

flash.

B. PFFS

To address the problems with YAFFS2, PFFS was

proposed

[4].

In

PFFS,

an

architecture

using

PRAM

and

NAND

flash

memory

is

employed.

In

this

file

system,metadata

are

separated

and

stored

in

the

PRAM

region,whereas

the

other

data

are

stored

in the NAND flash memory region, as shown in Fig. 10 (b).

Metadata separation has two advantages. First, the overhead

of

metadata

updates

is

reduced.

As

shown

in

Fig.

10

(a),YAFFS2

writes 2KB of a NAND flash page for each metadata update. As

the metadata are frequently updated and most of the metadata

updates are performed in several bytes, metadata updates with

YAFFS2 create many invalid pages. This leads to severe

performance degradation due to garbage collection.

However, PFFS writes metadata in units of bytes, as it

maintains metadata in the PRAM region as shown in Fig. 10

(b). Consequently, metadata separation by PFFS reduces the

number of page-writes on account of in- place updating and

byte-level updating. Second, PFFS requires only a short

mounting time and uses a fixed amount of memory, whereas

other

flash

file

systems

such

as

YAFFS2

require

a

considerable

amount of time to scan NAND pages to construct in-memory file

and directory structures.

However,

PFFS

is

also

a

general- purpose

file

system;

thus,it

does

not

sufficiently

consider

NLE

operations.

In

this

paper,to

effectively support NLE, NLE-FFS is proposed. It is based on

the architecture shown in Fig.3.