HCoop / hcoop / debian / openafs.git / blame
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1 | =head1 NAME |
| 2 | ||
| 3 | fs_bypassthreshold - get/set Cache Bypass file size threshold | |
| 4 | ||
| 5 | =head1 SYNOPSIS | |
| 6 | ||
| 7 | =for html | |
| 8 | <div class="synopsis"> | |
| 9 | ||
| 10 | B<fs bypassthreshold> S<<< [B<-size> <I<file size>>] >>> [B<-help>] | |
| 11 | ||
| 12 | B<fs bypassthresh> S<<< [B<-s> <I<file size>>] >>> [B<-h>] | |
| 13 | ||
| 14 | =for html | |
| 15 | </div> | |
| 16 | ||
| 17 | =head1 DESCRIPTION | |
| 18 | ||
| 19 | The B<fs bypassthreshold> command either changes the AFS client Cache | |
| 20 | Bypass file size threshold, or reports the current threshold. Normally, | |
| 21 | when an application tries to read data via the OpenAFS client, the client | |
| 22 | will fetch the required data from the fileserver, store the results in | |
| 23 | the local cache, and then serve the application request from the local | |
| 24 | cache. When the Cache Bypass feature is enabled, certain files will be | |
| 25 | read directly from the network, and the data will not be saved to the | |
| 26 | local cache. In some scenarios, this can provide a significant | |
| 27 | performance improvement, especially if the data is only read once. | |
| 28 | ||
| 29 | Currently, the only way to specify which files should bypass the cache | |
| 30 | and which files should not, is by file size. In the future, different | |
| 31 | mechanisms may exist for specifying which files should bypass the local | |
| 32 | cache and which should not. | |
| 33 | ||
| 34 | If B<-size> is not specified, B<fs bypassthreshold> just reports the | |
| 35 | current threshold and exits. | |
| 36 | ||
| 37 | =head1 CAUTIONS | |
| 38 | ||
| 39 | Cache Bypass is still considered an experimental feature. Even in stable | |
| 40 | releases of OpenAFS, it is not considered as stable as the rest of OpenAFS. | |
| 41 | ||
| 42 | =head1 OPTIONS | |
| 43 | ||
| 44 | =over 4 | |
| 45 | ||
| 46 | =item B<-size> <I<file size>> | |
| 47 | ||
| 48 | Specifies how large a file must be in order to enable Cache Bypass mode. | |
| 49 | If a file is larger than the specified file size (in bytes), reading from | |
| 50 | that file will bypass the local cache and be read directly from the | |
| 51 | network. A file size of -1 indicates that Cache Bypass should be disabled | |
| 52 | complete, so no files will enable Cache Bypass mode, no matter how large | |
| 53 | they are. | |
| 54 | ||
| 55 | By default, Cache Bypass is disabled. | |
| 56 | ||
| 57 | =item B<-help> | |
| 58 | ||
| 59 | Prints the online help for this command. All other valid options are | |
| 60 | ignored. | |
| 61 | ||
| 62 | =back | |
| 63 | ||
| 64 | =head1 OUTPUT | |
| 65 | ||
| 66 | The output format is identical whether or not B<-size> was specified. If | |
| 67 | B<-size> is specified, the bypass threshold is changed, and the output | |
| 68 | represents the new, changed, threshold. Otherwise the output represents | |
| 69 | the current threshold. | |
| 70 | ||
| 71 | =head1 EXAMPLES | |
| 72 | ||
| 73 | The following example turns on Cache Bypass with a threshold of 4KiB: | |
| 74 | ||
| 75 | % fs bypassthreshold 4096 | |
| 76 | Cache bypass threshold 4096 | |
| 77 | ||
| 78 | The following example disables Cache Bypass: | |
| 79 | ||
| 80 | % fs bypassthreshold -1 | |
| 81 | Cache bypass threshold -1 (disabled) | |
| 82 | ||
| 83 | The following example examines the current Cache Bypass threshold: | |
| 84 | ||
| 85 | % fs bypassthreshold | |
| 86 | Cache bypass threshold 4096 | |
| 87 | ||
| 88 | =head1 PRIVILEGE REQUIRED | |
| 89 | ||
| 90 | To set the bypass threshold, the issuer must be logged in as the local | |
| 91 | superuser C<root>. Otherwise, no privilege is required. | |
| 92 | ||
| 93 | =head1 COPYRIGHT | |
| 94 | ||
| 95 | Copyright 2012 Sine Nomine Associates | |
| 96 | ||
| 97 | This documentation is covered by the BSD License as written in the | |
| 98 | doc/LICENSE file. This man page was written by Andrew Deason for | |
| 99 | OpenAFS. |