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| 225 | </div> |
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| 226 | <h1> HDFS Quotas Guide</h1> |
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| 227 | <div id="minitoc-area"> |
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| 228 | <ul class="minitoc"> |
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| 229 | <li> |
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| 230 | <a href="#Name+Quotas">Name Quotas</a> |
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| 231 | </li> |
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| 232 | <li> |
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| 233 | <a href="#Space+Quotas">Space Quotas</a> |
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| 234 | </li> |
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| 235 | <li> |
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| 236 | <a href="#Administrative+Commands">Administrative Commands</a> |
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| 237 | </li> |
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| 238 | <li> |
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| 239 | <a href="#Reporting+Command">Reporting Command</a> |
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| 240 | </li> |
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| 241 | </ul> |
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| 242 | </div> |
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| 243 | |
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| 244 | |
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| 245 | <p> The Hadoop Distributed File System (HDFS) allows the administrator to set quotas for the number of names used and the |
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| 246 | amount of space used for individual directories. Name quotas and space quotas operate independently, but the administration and |
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| 247 | implementation of the two types of quotas are closely parallel. </p> |
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| 248 | |
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| 249 | |
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| 250 | <a name="N10010"></a><a name="Name+Quotas"></a> |
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| 251 | <h2 class="h3">Name Quotas</h2> |
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| 252 | <div class="section"> |
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| 253 | <p> The name quota is a hard limit on the number of file and directory names in the tree rooted at that directory. File and |
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| 254 | directory creations fail if the quota would be exceeded. Quotas stick with renamed directories; the rename operation fails if |
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| 255 | operation would result in a quota violation. The attempt to set a quota will still succeed even if the directory would be in violation of the new |
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| 256 | quota. A newly created directory has no associated quota. The largest quota is <span class="codefrag">Long.Max_Value</span>. A quota of one |
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| 257 | forces a directory to remain empty. (Yes, a directory counts against its own quota!) </p> |
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| 258 | <p> Quotas are persistent with the <span class="codefrag">fsimage</span>. When starting, if the <span class="codefrag">fsimage</span> is immediately in |
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| 259 | violation of a quota (perhaps the <span class="codefrag">fsimage</span> was surreptitiously modified), |
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| 260 | a warning is printed for each of such violations. Setting or removing a quota creates a journal entry. </p> |
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| 261 | </div> |
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| 262 | |
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| 263 | |
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| 264 | <a name="N10029"></a><a name="Space+Quotas"></a> |
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| 265 | <h2 class="h3">Space Quotas</h2> |
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| 266 | <div class="section"> |
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| 267 | <p> The space quota is a hard limit on the number of bytes used by files in the tree rooted at that directory. Block |
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| 268 | allocations fail if the quota would not allow a full block to be written. Each replica of a block counts against the quota. Quotas |
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| 269 | stick with renamed directories; the rename operation fails if the operation would result in a quota violation. A newly created directory has no associated quota. |
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| 270 | The largest quota is <span class="codefrag">Long.Max_Value</span>. A quota of zero still permits files to be created, but no blocks can be added to the files. |
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| 271 | Directories don't use host file system space and don't count against the space quota. The host file system space used to save |
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| 272 | the file meta data is not counted against the quota. Quotas are charged at the intended replication factor for the file; |
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| 273 | changing the replication factor for a file will credit or debit quotas. </p> |
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| 274 | <p> Quotas are persistent with the <span class="codefrag">fsimage</span>. When starting, if the <span class="codefrag">fsimage</span> is immediately in |
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| 275 | violation of a quota (perhaps the <span class="codefrag">fsimage</span> was surreptitiously modified), a warning is printed for |
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| 276 | each of such violations. Setting or removing a quota creates a journal entry. </p> |
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| 277 | </div> |
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| 278 | |
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| 279 | |
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| 280 | <a name="N10042"></a><a name="Administrative+Commands"></a> |
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| 281 | <h2 class="h3">Administrative Commands</h2> |
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| 282 | <div class="section"> |
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| 283 | <p> Quotas are managed by a set of commands available only to the administrator. </p> |
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| 284 | <ul> |
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| 285 | |
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| 286 | |
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| 287 | <li> |
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| 288 | <span class="codefrag">dfsadmin -setQuota <N> <directory>...<directory></span> |
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| 289 | <br> Set the name quota to be <span class="codefrag">N</span> for |
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| 290 | each directory. Best effort for each directory, with faults reported if <span class="codefrag">N</span> is not a positive long integer, the |
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| 291 | directory does not exist or it is a file, or the directory would immediately exceed the new quota. </li> |
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| 292 | |
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| 293 | |
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| 294 | <li> |
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| 295 | <span class="codefrag">dfsadmin -clrQuota <directory>...<director></span> |
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| 296 | <br> Remove any name quota for each directory. Best |
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| 297 | effort for each directory, with faults reported if the directory does not exist or it is a file. It is not a fault if the |
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| 298 | directory has no quota. </li> |
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| 299 | |
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| 300 | |
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| 301 | <li> |
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| 302 | <span class="codefrag">dfsadmin -setSpaceQuota <N> <directory>...<directory></span> |
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| 303 | <br> Set the space quota to be |
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| 304 | N bytes for each directory. This is a hard limit on total size of all the files under the directory tree. |
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| 305 | The space quota takes replication also into account, i.e. one GB of data with replication of 3 consumes 3GB of quota. N can also be specified with a binary prefix for convenience, for e.g. 50g for 50 gigabytes and |
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| 306 | 2t for 2 terabytes etc. Best effort for each directory, with faults reported if <span class="codefrag">N</span> is |
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| 307 | neither zero nor a positive integer, the directory does not exist or it is a file, or the directory would immediately exceed |
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| 308 | the new quota. </li> |
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| 309 | |
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| 310 | |
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| 311 | <li> |
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| 312 | <span class="codefrag">dfsadmin -clrSpaceQuota <directory>...<director></span> |
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| 313 | <br> Remove any space quota for each directory. Best |
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| 314 | effort for each directory, with faults reported if the directory does not exist or it is a file. It is not a fault if the |
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| 315 | directory has no quota. </li> |
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| 316 | |
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| 317 | |
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| 318 | </ul> |
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| 319 | </div> |
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| 320 | |
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| 321 | |
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| 322 | <a name="N10076"></a><a name="Reporting+Command"></a> |
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| 323 | <h2 class="h3">Reporting Command</h2> |
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| 324 | <div class="section"> |
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| 325 | <p> An an extension to the <span class="codefrag">count</span> command of the HDFS shell reports quota values and the current count of names and bytes in use. </p> |
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| 326 | <ul> |
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| 327 | |
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| 328 | |
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| 329 | <li> |
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| 330 | |
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| 331 | |
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| 332 | <span class="codefrag">fs -count -q <directory>...<directory></span> |
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| 333 | <br> With the <span class="codefrag">-q</span> option, also report the name quota |
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| 334 | value set for each directory, the available name quota remaining, the space quota value set, and the available space quota |
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| 335 | remaining. If the directory does not have a quota set, the reported values are <span class="codefrag">none</span> and <span class="codefrag">inf</span>. |
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| 336 | |
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| 337 | </li> |
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| 338 | |
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| 339 | |
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| 361 | 2008 <a href="http://www.apache.org/licenses/">The Apache Software Foundation.</a> |
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