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Page 1 of
John WongCTO
Twin Peaks Software Inc.
Mirror File System
A Multiple Server File System
Page 2 of
Multiple Server File System
• Conventional File System – EXT3/UFSand NFS– Manage files on a single server and its storage
devices
• Multiple Server File system– Manage files on multiple servers and their
storage devices
Page 3 of
Problems
• Single resource is vulnerable
• Redundancy provides a safety net
– Disk level => RAID
– Storage level => Storage Replication
– TCP/IP level => SNDR
– File System level => CFS, MFS
– System level => Clustering system
– Application => Database
Page 5 of
Local File System
Data
EXT3
Application 1
Application 2
Kernel Space
User Space
Disk Driver
EXT3 manages file on the local server’s storage devices
Page 6 of
Application Application
NFS (Client mount)
Application Application
Data
EXT3/UFS
NFSD
Network File SystemClient Server
NFS manages file on remote server’s storage devices
Page 7 of
rsync, tar
NFS (Clientmount)
Application Application
Data B
EXT3/UFS
NFSD
EXT3 | NFS
EXT3/UFS
Data B
Client Server
Application
Applications can only use either one, not both.
Page 8 of
• Combine these two file systems to manage file onboth local and remote servers storage devices
-- at the same time
-- in real time
EXT3 + NFS ??
Page 9 of
Application Application
Data
EXT3/UFS
Application Application
Data
EXT3/UFS
Passive MFS Server
MFS = EXT3 + NFSActive MFS Server
MFS
NFS
User Space
Kernel Space
Page 10 of
• MFS is a kernel loadable module
- loaded on top of EXT3/UFS and NFS
• Standard VFS interface
• Provide Complete Transparency - to users and applications - to underlining file systems
Building Block Approach
Page 12 of
• Building block approach
-- Building upon existing EXT3, NFS, NTFS, CIFS infrastructures
• No metadata is replicated
-- Superblock, Cylinder group, file allocation map are not replicated.
• Every file write operation is checked by file system
-- file consistency, integrity
• Live file, not raw data replication
-- The primary and backup copy both are live files
Advantages
Page 13 of
• Interoperability
-- Two nodes can be different systems
-- Storage systems can be different
• Small granularity
-- Directory level, not entire file system
• One to many or many to one replication
Advantages
Page 14 of
• Fast replication-- Replication in Kernel file system module
• Immediate failover-- No need to fsck and mount operation
• Geographically dispersed clustering
-- Two nodes can be separated by hundreds of miles
• Easy to deploy and manage-- Only one copy of MFS running on primary server is needed for replication
Advantages
Page 15 of
Why MFS?
• Better Data Protection
• Better Disaster Recovery
• Better RAS
• Better Scalability
• Better Performance
• Better Resources Utilization
Page 16 of
File System Framework
SOLARIS Internal, Core Kernel Architecture, Jim Mauro. Richard McDougall, PRENTICE HALL
Opticaldrive
Network
File System Operation calls
User Applications
System Call Interface
File Operation SystemCalls Other System calls
read
()
wri
te (
)
op
en (
)
clo
se (
)
mkd
ir (
)
rmd
ir (
)
link
()
ioct
l ()
crea
t ()
lsee
k ()
mo
un
t ()
um
ou
nt
()
Sta
tfs(
)
syn
c ()
Vnode interfaces VFS interfaces
UF
S (
2)
NF
S (
2)
VxF
S
HS
FS
QF
S
UF
S (
1)
NF
S (
1)
PC
FS P
CF
S
Data Data Data Data
File System Operation calls
Page 17 of
MFS FrameworkUser Applications
System Call Interface
File Operation System Calls File System Operation callsOther System calls
read ()
wri
te (
)
op
en (
)
clo
se (
)
mkd
ir (
)
rmd
ir (
)
link
()io
ctl
()
crea
t ()
lsee
k ()
mo
un
t ()
um
ou
nt
()
Sta
tfs(
)
syn
c()
Vnode interfaces VFS interfaces
UF
S(2
)
NF
S(2
)VxF
S
HS
FS
QF
S
UF
S(1
)
NF
S (
1)
PC
FS
PC
FS
Network Optical driveData Data Data Data
MFS
Vnode VFS interface
Page 18 of
• Transparent to users and applications
- No re-compilation or re-link needed
• Transparent to existing file structures
- Same pathname access
• Transparent to underlying file systems
- UFS, NFS
Transparency
Page 19 of
• Conventional Mount
- One directory, one file system
• MFS Mount
- One directory, two or more file systems
Mount Mechanism
Page 20 of
# mount –F mfs host:/ndir1/ndir2 /udir1/udir2
- First mount the NFS on a UFS directory
- Then mount the MFS on top of UFS and NFS
- Existing UFS tree structure /udir1/udir2becomes a local copy of MFS
- Newly mounted host:/ndir1/ndir2 becomes aremote copy of MFS
- Same mount options as NFS except no ‘-o hard’option
Mount Mechanism
Page 21 of
# /usr/lib/fs/mfs/mfsck mfs_dir
- After MFS mount succeeds, the local copy maynot be identical to the remote copy.
- Use mfsck (the MFS fsck) to synchronize them.
- The mfs_dir can be any directory under MFSmount point.
- Multiple mfsck commands can be invoked at thesame time.
MFS mfsck Command
Page 22 of
READ/WRITE Vnode Operation
• All VFS/vnode operations received by MFS
• READ related operation: read, getattr,…. those operations only need to go to local copy
(UFS).
• WRITE related operation: write, setattr,…..those operations go to both local (UFS) and remote(NFS) copy simultaneously (using threads)
Page 23 of
• Directory Level
- Mirror any UFS directory instead of entire UFSfile system
- Directory A mirrored to Server A
- Directory B mirrored to Server B
• Block Level Update
- Only changed block is mirrored
Mirroring Granularity
Page 24 of
# /usr/lib/fs/mfs/msync mfs_root_dir
- A daemon that synchronizes MFS pair after aremote MFS partner fails.
- Upon a write failure, MFS:
- Logs name of file to which the write operation failed
- Starts a heartbeat thread to verify the remote MFSserver is back online
- Once the remote MFS server is back online, msyncuses the log to sync missing files to remote server.
MFS msync Command
Page 25 of
Active/Active ConfigurationServer Server
Application Application
Data A
UFS
Application Application
Data B
UFS
Active MFS Server
MFS MFS
Active MFS Server
NFS NFS
Page 26 of
MFS uses UFS, NFS file record lock.
Locking is required for the active-activeconfiguration.
Locking enables write-related vnode operations asatomic operations.
Locking is enabled by default.
Locking is not necessary in active-passiveconfiguration.
MFS Locking Mechanism
Page 27 of
• Real-time
-- Replicate file in real-time
• Scheduled
-- Log file path, offset and size
-- Replicate only changed portion of a file
Real -Time and Scheduled
Page 28 of
• Online File Backup
• Server File Backup, active passive
• Server/NAS Clustering, active Active
Applications
Page 29 of
Application Application
Data
NTFS
Application Application
Data
NTFS
Remote Server
MFS = NTFS + CIFS
Window Desktop/Laptop
MFS
CIFS
Page 30 of
MFS
UserDesktop/Laptop
Online File BackupReal-time or Scheduled time
Folder
ISP Server
MFS
Folder
MFS
Folder
LAN or WanLAN or Wan
Page 31 of
Secondary
Server Replication
Mirror FileSystem
Mirror FileSystem
App
Primary
Mirror FileSystem
Mirroring Path : /home
: /var/spool/mail
Heartbeat