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File dolly.md of Package dolly
%DOLLY(1) Version 0.59 | Dolly file transfer DOLLY ===== A program to clone disks / partitions SYNOPSIS ======== |dolly | \[**-f** config\] 24 March 2005 DESCRIPTION =========== Dolly is used to clone the installation of one machine to (possibly many) other machines. It can distribute image-files (even gnu-zipped), partitions or whole hard disk drives to other partitions or hard disk drives. As it forms a "virtual TCP ring" to distribute data, it works best with fast switched networks (we were able to clone a 2 GB Windows NT partition to 15 machines in our cluster over Gigabit Ethernet in less than 4 minutes). As dolly clones whole partitions block-wise it works for most filesystems. We used it to clone partitions of the following type: Linux, Windows NT, Oberon, Solaris (most of our machines have multi boot setups). We have a small (additional) Linux installation on all of our machines or use a small one-floppy-disk-linux (e.g. muLinux) to do the cloning. On newer machines we use PXE to boot a small system in a RAM disk. From that system we then clone the hard disks in the machines. Configuration file ------------------ You need a configuration file for the cloning process. Its format is strict, but easy. It contains the following entries (note that the order of the entries is fix): (The text after "Syntax:" explains the syntax of the entry, the lines following "EG:" are example lines) 1. The file/partition you want to clone, preceeded by the keywords "infile" or "compressed infile" in case of a compressed image. This file or partitions needs to be available on the master only. Dolly will warn you if you try to use a compressed infile which does not end with ".gz". The compressed keyword is important so that the master can inform the clients when they have to use gunzip before writing a file. The optional keyword "split" after the filename instructs Dolly to read all files with the given name and an appended number, separated by an underscore. Syntax: [compressed] infile <input file or device> [split] EG: infile /dev/sda10 Will just send the partition /dev/sda10 to all clients. EG: compressed infile /images/cloneimages/sda10_WinNTRes.gz Will send the given file compressed to all the clients, instructing them to uncompress the image before writing it. EG: infile /images/cloneimages/sda split Will send all files of the form /images/cloneimages/sda_<number> in order to the clients. EG: compressed infile /images/cloneimages/sda.gz split Will send all files of the form /images/cloneimages/sda.gz_<number> in order to the clients, instructing them to decompress the incoming stream before writing it. 2. The file or partition you want to write (usually its a partition, but you can also write to a file) after the keyword "outfile". This file needs to be available on the clients only. The optional keyword "compressed" instructs the server to compress the data before sending it, so the client will store the data compressed. The optional keyword "split" after the filename, followed by a number and a multiplier, instructs the client to write the data in junks of no more than the given size. This is useful if the file system on your client does not allow files greater than a certain size. The files will be stored with the given namen and an appended "_<number>". Syntax: [compressed] outfile <output file or device> [split <n>(k|M|G|T)] EG: outfile /dev/sda10 Will store the incoming data stream to the partition sda10. EG: compressed outfile /images/cloneimages/sda10_SuSE81.gz Will store the compressed data stream in the given file. EG: compressed outfile /images/cloneimages/sda_all.gz split 2G Will store the incoming compressed data stream in the directory /images/cloneimages/ in files sda_all.gz_0, sda_all.gz_1 and so on. -. Instead of the first two entries ("infile" and "outfile") it is also possible to use the single line "dummy [<MB>]", where <MB> is the number of Megabytes to transfer in dummy mode. If <MB> is set to 0, then the clients will just terminate. This is useful when benchmarking with different options, so the clients can run all the time. To finally terminate them on all clients, just set dummy to 0. NOTE: It is probably better to use the newer "-t" switch on the server to specify the number of seconds the benchmarks should run. In that case you can leave the <MB> blank. Syntax: dummy [<MB>] EG: dummy 128 -. The optional keyword "segsize" is mostly used to benchmark switches. It specifies the maximal size of TCP segments during the network transfer. Usually you don't need to specify this option at all. Syntax: segsize <TCP_MAXSEG size> EG: segsize 128 -. With the optional keyword "add" it is possible to add more interfaces to use. The network traffic is then evenly distributed across the interfaces. This option is useful if you have for example two fast ethernet interfaces in your machines: One for administrative purposes and one for your main application on the cluster. This option is not so useful if you have multiple interfaces with different bandwidths. In this case just use the fastest available. You have to specify the number of additional interfaces and the suffixes of thouse interfaces. For example, in a cluster where the machines are named slave0..slave15 on their default interfaces and all the machines have a second interface named slave0-fast..slave15-fast, you should use the line specified below (EG). Syntax: add <nr>:<suffix>{:<suffix>} EG: add 1:-fast -. The optional keyword "fanout" was mostly used during performance tests of different network topologies. You barely need it in practice. Fanout specifies the number of outlinks from the server and the following machines (except the leafes). A fanout of 1 is a linear list (the default behaviour of Dolly and usually the fastest), 2 is a binary tree, 3 is a ternary tree, etc. Dolly automatically connects all the specified clients with the desired topology. Syntax: fanout <fanout> EG: fannout 1 -. The optional keyword "hypennormal" instructs Dolly to treat the '-' character in hostnames as any other character. By default the hyphen is used to separate the base hostnames from the names of the different interface (e.g. "node12-giga"). You might use this paramater if your hostnames include a hypen (like e.g. "node-12"). Syntax: hyphennormal EG: hyphennormal 3. After the keyword "server" follows the hostname of the server (or master). This is required for the last machine in the ring to be able to send the end-acknowledge back to the server. Syntax: server <master machine> EG: server cluster-master 4. This entry has the keyword "firstclient" followed by the hostname of the first client in the ring. You should use the hostname of the machine here, not the name of the interface where you want to connect. Syntax: firstclient <name of first machine> EG: firstclient cluster-1 5. This entry has the keyword "lastclient" followed by the hostname of the last client in the ring. You should use the hostname of the machine here, not the name of the interface where you want to connect. Syntax: lastclient <name of last machine> EG: lastclient cluster-9 6. This entry specifies how many clients are in the ring. The keyword is "clients" followed by the actual number of clients. This number does not include the master. Syntax: clients <number of clients> EG: clients 9 7. The following lines contain the interface-names of the client machines. The number of machines must match the above number of clients (see 6.). You should use the name of the interface on which the machines will receive the data. Syntax: <name of client 1> <name of client 2> [...] <name of client n> EG: cluster-1-giga cluster-2-giga [...] cluster-9-giga 8. The last entry in the config file consists of the keyword "endconfig" and marks the end of the configuration file. Syntax: endconfig EG: endconfig Note on nodes' hostnames ------------------------ On some machines (e.g. with very small maintenance installations), gethostbyname() does not return the hostname (I don't know why). If you have that problem, you should make sure that the environment variables MYNODENAME or HOST are set accordingly. Dolly first tries to get the environment variable MYNODENAME, then HOST, then it tries gethostbyname(). This feature was introduced in dolly version 0.58. OPTIONS ============= Dolly has a few options which are explained here: -h : Prints a short help and exits. -V : Prints the version number as well as the date of that version and exits. -v : This switches to verbose mode in which dolly prints out a little bit more information. This option is recommended if you want to know what's going on during cloning and it might be helpful during debugging. -s : This option specifies the server machine and should only be used on the master. Dolly will warn you if the config file specifies another master than the machine on which this option is set. This option must be secified before the "-f" option! -S : Same as "-s", but dolly will not warn you if the server's hostname and the name specified in the config file do not match. -q : Usually dolly will print a warning when the select() system call is interrupted by a signal. This option suppresses these warnings. -c : With this option it is possible to specify the uncompressed size of a compressed file. It's only needed for performance statistics at the end of a cloning process and not important if you are not interested in the statistics. -d : The "Dummy" option disables all disk accesses. It can be used to benchmark the throughput of your system (computers, network, switches). This option must be specified before the "-f" option! -t <seconds> : When in dummy mode, this option allows to specify how long the testrun should approximately take. Since the dummy mode is mostly used for benchmarking purposes and single runs might result in different speeds (especially with many machines and bad switches or with small TCP segment sizes), it's more convenient to specify the run-lenght in seconds, as the benchmark-time becomes more predictable. -f <config file> : This option is used to select the config file for this cloning process. This option makes only sense on the master machine and the configuration file must exist on the master. -o <logfile> : This option specifies the logfile. Dolly will write some statistical information into the logfile. it is mostly used when benchmarking switches. The format of the lines in the logfile is as follows: Trans. data Segsize Clients Time Dataflow Agg. dataflow [MB] [Byte] [#] [s] [MB/s] [MB/s] -a <timeout> : Sometimes it might be useful if Dolly would terminate instead of waiting indefinitely in case something goes wrong. This option lets you specify this timeout. If dolly could not transfer any data after <timeout> seconds, then it will simply print an error message and terminate. This feature might be especially useful for scripted and automatic installations (such as "CloneSys"), where you don't want to have dolly-processes hang around if a machine hangs. -n : Do not sync() before exit. Thus, dolly will exit sooner, but data may not make it to disk if power fails soon after dolly exits. -u <size> : Specify the size of buffers for TCP sockets. Should be a Multiple of 4K. -b <size> : option to specify the TRANSFER_BLOCK_SIZE. Should be a multiple of the size of buffers for TCP sockets. How it works ============ Setting up or upgrading a cluster of PCs typically leads to the problem that many machines need the exact same files. There are different approaches to distribute the setup of one "master" machine to all the other machines in the cluster. Our approach is not sophisticated, but simple and fast (at least for fast switched networks). We send the data around in a "virtual TCP ring" from the server to all the clients which store tha received data on their local disks. One machine is the master and distributes the data to the others. The master can be a machine of the cluster or some other machine (in the current version of dolly it should be the same architecture though). It stores the image of the partition or disk to be cloned or has the partition on a local disk. The server should be on a fast switched network (as all the other machines too) for fast cloning. All other machines are clients. They receive the data from the ring, store it to the local disk and send it to the next machine in the ring. It is important to note that all of this happens at the same time. The cloning process is depicted in the following two figures. Usually there are more than two clients, but you get the idea: +========+ +==========+ +==========+ | Master | | Client 1 | | Client 2 | +====+===+ +===|======+ +====+=====+ \ | / \ +===+====+ / +===+ Switch |=====+ +========+ Cloning process, physical network +========+ Data +==========+ Data +==========+ | Master |========>| Client 1 |=======>| Client 2 | +========+ +==========+ +==========+ ^ | | | Data | Data | Data | V V +======+ +======+ +======+ | Disk | | Disk | | Disk | +======+ +======+ +======+ Cloning process, virtual network with TCP connections We choose this method instead of a multicast scheme because it is simple to implement, doesn't require the need to write a reliable multicast protocol and works quite well with existing technologies. One could also use the master as an NFS server and copy the data to each client, but this puts quite a high load on the server and makes it the bottleneck. Furthermore, it would not be possible to directly clone partitions from one machine to some others without any filesystem in the partition. Different cloning possibilities ------------------------------- There are different possibilities to clone your master machine: - You already have an image of the partition which you want to clone on your master (raw or compressed). In this case you need Linux (some other UNIX might also work, but we haven't tested that yet) on your master and a Linux on each client. - You want to clone a partition which is on a local disk of your master. In this case you need Linux (or probably another UNIX, we haven't tried that) on your master as well as on all the clients. You can use any Linux installation as long as it's not the one you want to clone (i.e. you can not clone the Linux which you are currently running in. See the warning below). - You want to clone a whole disk including all the partitions. In this case you either need a second disk on all machines where your Linux used for the cloning process runs on (not the one you want to clone) or you need a small one-floppy-disk-Linux which you boot on all machines. In the later case you also need dolly on all machines (copy it to your floppy disk or mount it with NFS) and the config-file on the master. WARNING: You can NOT clone an OS which is currently in use. That is why we have a small second Linux installation on all of our machines (or a small system that can be booted over the network by PXE), which we can boot to clone our regular Linux partition. CHANGES ======= version 0.2 ------------------ We applied some changes to Dolly since version 0.2. Most of them are not very important. - Dolly as a benchmarking tool. Dolly can now be used to benchmark your network. In the dummy mode, Dolly will not access the hard disk, neither for reading nor for writing. It just transfers data between your machines. This might be useful for testing the throughput of your switch. The running time for such a run can be specified with the "-t" option on the command line. With the "-o" option you can specify a logfile where Dolly will write some statistical information. - Using extra network interfaces. It's now possible to use multiple network interfaces for the data transfer. This is mostly useful if you have multiple network interfaces with similar speeds, e.g. two fast ethernet networks (one for administration/logins and the other for your applications communication). For example: If your machines are connected with two fast ethernet links, then you should be able to increase the thourghput of the cloning process from 10 to 20 MB/s, therefore cutting the cloning-time by half. You need the "add" option in the config file to use this feature. WARNING: This feature has only been tested with the linear network topology (no fanout option or "fanout 1" option in the config file). - Different networking topologies. We tried different topologies (binary trees, ternary trees, ...) to get somre more results in a paper, but the initial multi-drop chain (virtual TCP ring) is still the best. You will most likely not need this feature. version 0.57 ------------ Besides some bug-files and smaller improvements, it's now possible to split an image in multiple files for archival and send the multiple-file image to the clients. This allows to story arbitrary long partitions on file systems with a file size limit. For details and examples, see the section about the configuration file below (parameters infile and outfile). version 0.58 ------------ Thanks to David Mathog, dolly is now able to read or write data from its standard input or to its standard output. That means that you can e.g. pipe a tar stream through dolly. Whether that feature is useful or not depends on your situation. By using tar (instead of cloning the whole partition) your disks' reads and writes will be slower, but you only transfer the data that is actually needed. This feature might be most useful in situations where e.g. your disks/partitions are mostly empty or have different sizes/geometries. Please note that version 0.58 has not yet been thoroughly tested (I'm no longer working with clusters). E.g. it is not yet clear what happens when somebody tries to reach you with the "write", "talk" or "wall" commands while dolly is running (which might potentially interfere with with your stdin/stdout, see below). Note also, that since all of dolly's output is now written to stderr (instead of stdout as before), some third-party scripts might no longer work. To use the feature, you should specify /dev/stdin as your infile and/or /dev/stdout as your outfile. version 0.58C ------------- Again, thanks to David Mathog, dolly can now be run without explicit sync() at the end of the cloning process (option "-n"). This can speed up dolly's runtime considerably when cloning smaller files, but there is no garantuee that the data actually made it to the disk if there is e.g. a power loss right after dolly finished. version 0.59 ------------ Some output improvments and add some options to deal with socket and buffer size to experiment some parameter on the fly. Done some cleanup in the C code to get less warning in building with recent GCC7. EXAMPLE ======= In this example we assume a cluster of 16 machines, named node0..node15. We want to clone the partition sda5 from node0 to all other nodes. The configuration file (let's name it dollytab.cfg) should then look as follows: infile /dev/sda5 outfile /dev/sda5 server node0 firstclient node1 lastclient node15 clients 15 node1 node2 node3 node4 node5 node6 node7 node8 node9 node10 node11 node12 node13 node14 node15 endconfig Next, we start Dolly on all the clients. No options are required for the clients (but you might want to add the "-v" option for verbose progress reports). Finally, Dolly is started on the server as follows: dolly -v -s -f dollytab.cfg That's all. Bibliography ============ Felix Rauch, Christian Kurmann, Thomas M. Stricker: <em>Optimizing the distribution of large data sets in theory and practice</em>. Concurrency and Computation: Practice and Experience, volume 14, issue 3, pages 165-181, april 2002. (c) John Wiley & Sons, Ltd. Maintained by Felix Rauch. http://www.cs.inf.ethz.ch/~rauch/ Felix Rauch <rauch@inf.ethz.ch> AUTHORS ======= Antoine Aginies <agines@suse.com> Christian Goll <cgoll@suse.com>
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