7 Distributed File Systems

Transcription

1 Single tree /etc Global File system /progs Drives mounted over the network to create a single tree /user /sys Network Forest of drives 7 Distributed File Systems C: D: E: F: Drives mounted over the network to a forest of drives

2 7.1 Advantages of distributing files Many users can have access to a single source of information. Several copies of the same information can be stored, and when any one of them is updated they are synchronized to keep each of them up-to-date. Users can have access to a local copy of data, rather than accessing a remote copy of it. Large file systems can be built from a network of connected disk drives. Administrators can easily view the complete file system. Interlinking of databases to create large databases, which can be configured for a given application.

3 7.2 Distributed File Systems Administration services Mounted as a local drive Localized File storage (rather than accessing a remote file) Networked file system (NFS) Network Distributed databases Centralized Configuration (passwords, user IDs, and so on)

4 7.3 Tree or Forest Single tree /etc Global File system /progs Drives mounted over the network to create a single tree /user /sys Forest of drives C: D: E: F: Network Drives mounted over the network to a forest of drives

5 7.4 Advantages of global file system The structure of the file system, and the drives that are mounted are transparent to the user. As far as the user is concerned the complete file system is viewable. Every user can view the complete file system, if required. The file system is consistent around the network, and can be setup on a per computer basis.

6 7.5 Advantages of forest of disks It is easier to determine if the remote drive is mounted, as it will appear as a mounted resource. With a single tree it is often difficult to determine if a drive is loaded onto the global file system as the basic structure still exists. Less complex than a global file, and easier to mount drives, but can become complex to setup if there are many remote drives to be mounted.

7 7.6 Data representation (XDR format) Problems with data representation: different number of bits used to store data type and different methods of storing (Little-endian where least-significant byte is stored last - Intel architecture, and big-endian where the leastsignificant byte is store first - Motorola architecture). Four standard formats: Unsigned and signed integer, single-precision floating point, double-precision floating point and strings. Signed format uses 2 s complement, floating point uses IEEE format (1 sign bit, eight bits for the exponent and 23 bits of the base-2 fractional part).

8 7.7 NDS and OSI model GetAttr() SetAttr() Application NIS NFS Presentation Session Transport Network Data link Physical XDR RPC TCP IP Ethernet/ Token ring String integer floating-point Nfs (100003) Read() Write() Create() Remove() Rename() Link() SymLink() MkDir() RmDir() ReadDir()

9 NFS server Remotely accessed file system RPC procedures getattr, setattr, read, write, create, remove, rename, link, symlink, mkdir, rmdir, readdir File system either mounted onto a single tree or as a forest of drives Network RPC response Requested data, parameters or status flag (such as: NFS_OK and NFSERR_PERM) NFS client

10 7.9 NIS (Network Information Services) Allows for centralized configuration of system configuration files. Supports a client-server architecture, with the use of primary and secondary NIS severs. Keeps centralized copies of important files, such as: password file (for storing passwords). groups file (for group information). hosts file (for DNS information) and so on. rpc file. services file.

11 7.10 NIS Clients #/etc/protocols #/etc/protocols ip 0 IP ip 0 IP icmp 1 ICMP icmp 1 ICMP ggp 3 GGP ggp 3 GGP tcp 6 TCP tcp 6 TCP Server NIS Domain Master NIS server maintains: /etc/passwd Domain passwords /etc/groups Domain groups /etc/hosts IP addresses and host names /etc/rpc RPC processes /etc/network Used to map IP address to networks /etc/protocols Known network layer protocols /etc/services Known transport layer protocols #/etc/hosts #/etc/groups #/etc/hosts #/etc/groups bath root::0:root bath root::0:root compuserve other::1:root,hpdb compuserve other::1:root,hpdb niss bin::2:root,bin niss bin::2:root,bin hensa sys::3:root,uucp hensa sys::3:root,uucp janet freds_grp::4:fred,fred2,fred janet freds_grp::4:fred,fred2,fred3 #/etc/passwd #/etc/passwd root:fdec6.32:1:0:super unser:/user:/bin/csh root:fdec6.32:1:0:super unser:/user:/bin/csh fred:jt.06hldisdaa:2:4:fred Blogs:/user/fred:/bin/csh fred:jt.06hldisdaa:2:4:fred Blogs:/user/fred:/bin/csh fred2:jty067sdisfaa:3:4:fred Smith:/user/fred2:/bin/csh fred2:jty067sdisfaa:3:4:fred Smith:/user/fred2:/bin/csh #/etc/services #/etc/services #/etc/networks ftp 21/tcp #/etc/networks #/etc/rpc ftp 21/tcp loopback #/etc/rpc telnet 23/tcp loopback portmapper portmap sunrpc telnet 23/tcp localnet portmapper portmap sunrpc smtp 25/tcp localnet rstatd rstat rstat_svc smtp 25/tcp Production rstatd rstat rstat_svc pop3 110/tcp Production rusersd rusers pop3 110/tcp rusersd rusers nfs nfsprog nfs nfsprog ypserv ypprog ypserv ypprog

12 Master NIS Server maintains: /etc/passwd /etc/groups /etc/hosts /etc/rpc /etc/network /etc/protocols /etc/services and so on. Master sends updates to NIS slaves Slave NIS server

13 The superuser then logs into the client and creates a mount point /win (empty directory). % mkdir /mnt The remote directory can then be mounted with: % mount miranda:/user /win NFS maintains the file /etc/mnttab which contains a record of the mounted file systems. The general format is: special_file_name dir type opts freq passno mount_time cnode_id where mount_time contains the time the file system was mounted using mount. Sample contents of /etc/mnttab could be: /dev/dsk/c201d6s0 / hfs defaults /dev/dsk/c201d5s0 /win hfs defaults castor:/win /net/castor_win nfs rw,suid miranda:/win /net/miranda_win nfs rw,suid spica:/usr/opt /opt nfs rw,suid triton:/win /net/triton_win nfs rw,suid In this case there are two local drivers (/dev/dsk/c201d6s0 is mounted as the root directory and /dev/dsk/c201d5s0 is mounted locally as /win). There are also four remote directories which are mounted from remote servers (castor, miranda, spica and triton). The directory mounted from castor is the /win directory and it is mounted locally as /net/castor_win. hfs defines a UNIX format disk and nfs defines that the disk is mounted over NFS.

14 7.13 Daemons biod which is asynchronous block I/O daemons for NFS clients. inetd which is an Internet daemon that listens to service ports. It listens for service requests and calls the appropriate server. The server it calls depends on the contents of the /etc/inetd.conf file. nfsd which is the NFS server daemon. It is used by the client for reading and writing to a remote directory and it sends a request to the remote server nfsd process. pcnfsd which is a PC user authentication daemon. portmap which is an RPC program to port number conversion daemon. When a client makes an RPC call to a given program number, it first contacts portmap on the server node to determine the port number where RPC requests should be sent.

15 Inetd.conf # <service_name> <sock_type> <proto> <flags> <user> <server_path> <args> # # Echo, discard and daytime are used primarily for testing. echo stream tcp nowait root internal echo dgram udp wait root internal discard stream tcp nowait root internal discard dgram udp wait root internal daytime stream tcp nowait root internal daytime dgram udp wait root internal time dgram udp wait root internal # # These are standard services. ftp stream tcp nowait root /usr/sbin/tcpd /usr/sbin/wu.ftpd telnet stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.telnetd # # Shell, login, exec and talk are BSD protocols. shell stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.rshd login stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.rlogind #exec stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.rexecd talk dgram udp wait root /usr/sbin/tcpd /usr/sbin/in.ntalkd ntalk dgram udp wait root /usr/sbin/tcpd /usr/sbin/in.ntalkd # # Pop mail servers pop3 stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.pop3d