FileSystems Architecture Introduction

1. RaleighFS | RaleighDB
A bs tra c t St o rag e La ye r

2. What is a File-Systems
Is a Method of storing and organizing data
to make it easy to find and access.
...to interact with an object
You name it, and you say
what you want it do.
The Filesystem takes the name you give
Looks through disk to find the object
Gives the object your request to do
something.
Image taken from namesys Reiser4

3. What is a File-Systems
On Disk Format (...serialized struct)
ext2, ext3, reiserfs, btrfs...
Namespace
(Mapping between name and content)
/home/th30z/, /usr/local/share/test.c, ...
Runtime Service: open(), read(), write(), ...

4. ...A bit of History
Multics 1965 (File-System Paper)
A General-Purpose File System For Secondary Storage
Unix Late 1969
Sun Microsystem 1984
2010 ...Till Now, no significant changes
User Program
User Space
Kernel Space
System Call Layer
Vnode/VFS Layer
FS 1 FS 2 FS 3 FS 4 ... FS N

5. The File-System
A file is something that tries creat(path, mode)
to look like a sequence of bytes.
open(path, flags)
You can read the bytes, and write the bytes.
pread(fd, buffer, nbytes, offset) You can specify what byte
to start to read/write from,
pwrite(fd, buffer, nbytes, offset) and the number of bytes to read/write.
Cutting bytes out of the middle ftruncate(fd, length)
or the beginning of a file,
and inserting bytes into the middle of a file,
are not permitted!
Metadata (ctime, mtime, mode, ...)
(Block Pointers)
(Data Blocks)

6. Decompose a File-System

7. Semantic Layer
User Request
...to interact with an object
You name it, and you say
Resolve
Semantic Layer what you want it do.
(Path/Query to Key)
For the end user this name has a meaning and this
Lookup Key meaning should be captured by the Semantic Layer,
while the rest of the Storage Layer is not interested
in the meaning of the name.
Metadata User defined name has generally a variable length and
Semantic Layer
Lookup Metadata from Key tends to be verbose, while the storage layer needs
something fixed size and short, to ensure a quick lookup.
To do this, objects names are converted in keys that can be
Object Pointer a simple hash of the name or something more elaborated.
for Read/Write
Requests

8. Semantic Layer
User Request
Resolve The semantic layer takes names
Semantic Layer
(Path/Query to Key) and converts them into keys,
the Storage Layer take keys
Lookup Key
and finds the objects
Metadata
Semantic Layer
Operations
Lookup Metadata from Key
create(): Create a new object, Unix place this object in
parent directory object, Set Unix Stat, ...
open(): Open specified object.
lookup(): Lookup Key of specified object.
Object Pointer move(): Change name or location of specified object.
for Read/Write unlink(): specified object, Unix remove this object
from parent directory object.
Requests

9. Semantic Layer
unix Seman ti c
root ‘/’ is the entry point
Every object
must be in one directory
Parse Object Name
traverse each directory
check permission
and open it.

10. Semantic Layer
Flat S emant ic
Same Level
for every Objects
No Directory No forced Hierarchy
Traversal open(‘mytable’)
Lookup item open(‘office-documents/stats’)
just by name
A B+Tree can be used
to map Object Key
to its Metadata
Root node Internal nodes Leaf nodes (Stat/Meta data)

11. Object Layer
An object
contains Different Data Mimic
your data Types have Languages Types
different set, dict, list, ...
methods and
needs
Log Object (Append Only) Operations
KV Object (Hashtable) create(): Initialize object data structure for creation.
open(): Initialize object data structure for open.
Set Object (Think at Dirs) close(): Uninitialize object data structure.
Flow Object (Write Anywhere) read():
write():
Read specified object data.
Write specified data to object.
Table Object (Database Table) append():
remove():
Append Data to object.
Remove specified data from object.
Record Object (C Struct) truncate(): Truncate or extend object to specified length.
inject(): Inject block data to a specified object.
... chop(): Remove block data from specified object.

12. Flow Object
Extent list,
Pointers to data... Insert/Remove
Block Every-Where
• read(offset, length)
• write(offset, length)
Like a regular ‘80s file
• inject(offset, length)
but with more flexibility
• remove(offset, length)
• truncate(size)

13. Dir Object
Pages list,
Object Names... Keep track
Object-A
Object-A
of objects stored
Object-B
Object-C Object-X
... table/users Object-Y
(names)
table/addrs Object-Z
... ...
• read(index, n)
Semantic Layer
• append(name)
doesn’t guarantee
• remove(index) to keep Objects Names
• remove(name)
Wait! Wait! Dir Object is just a Set!

14. RecNo Object
Extent Record list,
Pointers to data... Insert/Remove
Record Every-Where
• read(recno)
Like Flow Object
• write(recno) but with a fixed size
• inject(recno) user defined structure
• remove(recno)
• truncate(n) Metadata keep tract
fields sizes and names

15. Device Layer
Where data is Stored?
Memory Block Allocation
Disk (Raid?) Bitmap
Somewhere (DFS) Extents?
Blocks
Fixed Size
Variable Size
Operations
alloc(): Allocate a block (touch bitmap/space-map)
Different Layout
dealloc(): Deallocate a block (touch bitmap/space-map)
for different types
read(): Read some data from disk
write(): Write data on disk
for different workloads
insert(): Insert Key/Value to the B+Tree
remove(): Remove Key/Value from the B+Tree
lookup(): Retrive Key Value from the B+Tree

16. Device Layer
kee p tr ac k o f Bl o ck s
What do you need?
Small Variable Size Files (B+Tree)
Large Variable Size Files (Extents)
Best case Worst case ‘Normal’ case
Contiguous One block Large or Tail
Root node Internal nodes Extent nodes Raw Data (leaf/blob)
(Block Pointers)
Choose your Block
4k, 16k, 64M
(Data Blocks)

17. Device Layer
B a ck Ref eren ce s
why fsck takes the whole day?
Who owns the block X?
Metadata (ctime, mtime, mode, ...)
(Block Pointers)
(Data Blocks)
Put a back Ref into Data blocks!
Metadata (ctime, mtime, mode, ...)
(Block Pointers)
(Data Blocks)

18. RaleighFS Structure
RPC Server
Observers
register
RaleighFS unregister
notify
create
open
sync
Semantic Layer Objects Device Layer
Flat Unix Memory Files Disk
Flow Set Map
create create read
SeqMap RecNo Table insert
open move open write
remove
close unlink close alloc
lookup
sync create sync dealloc
insert
open query update
close ioctl append
sync remove

19. RaleighFSv5
Matteo Bertozzi
2005-2010
A b s t r a c t S t o r a g e L a y e r
To interact with an Object create
you name it, and you say open insert
what you want it do. close update
sync append
Semantic Layer lookup
key
remove
query
move ioctl
Objects Layer unlink
sync insert
Device Layer read
write
alloc
dealloc
remove
lookup

20. Q&A
RaleighFSv5
Matteo Bertozzi
2005-2010
A b s t r a c t S t o r a g e L a y e r
To interact with an Object create
you name it, and you say open insert
what you want it do. close update
sync append
Semantic Layer lookup
key
remove
query
move ioctl
Objects Layer unlink
sync insert
Device Layer read
write
alloc
dealloc
remove
lookup