I was recently tasked to develop a system that would need to write data in the Gigabytes per second range directly to disk. While doing so, I needed to spec out and build a machine that allowed for that type of bandwidth to be persisted as well as find the most optimized filesystem and write method available in C. Once the specs were done and the machine arrived, it was time to determine which filesystem and write method under Linux would give the best results for writing. I initially tested with bonnie++, but soon became aware that the results I was receiving were not a true test of the raid configuration and filesystem, but were instead block writes and reads. For my purposes I need to benchmark the write speed of several different writing types including asynchronous writing, standard IO and generic (open,write,read) IO. To do so, I created a simple writetest program:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 | #include <aio.h>#include <time.h>#include <stdio.h>#include <malloc.h>#include <stdlib.h>#include <string.h>#include <errno.h>#include <sys/stat.h>#include <sys/mman.h>#include <math.h>int nVersionMajor = 1;int nVersionMinor = 0;int nVersionBuild = 1;int64_t mb = 1048576;char szOutputDir[1024];long nSize = 0;int nIteration;short nUseAio;short nUseStd;short nUseGen;unsigned long long nStdioAvg = 0;unsigned long long nAioAvg = 0;unsigned long long nGenAvg = 0;double nSec = 1000000.0;char * pBytes;void stdioWrite(char * filename){FILE * pFile;struct timeval tvStart;struct timeval tvEnd;int64_t nEnd;int64_t nStart;gettimeofday(&tvStart);nStart = tvStart.tv_sec * 1000000 + tvStart.tv_usec;pFile = fopen(filename,"w");if(!pFile){fprintf(stderr, "[Error] could not open %s for writing.n", filename);exit(1);}//end iffwrite(pBytes, strlen(pBytes), 1, pFile);fclose(pFile);gettimeofday(&tvEnd);nEnd = tvEnd.tv_sec * 1000000 + tvEnd.tv_usec;nStdioAvg += (nEnd-nStart);printf("stdio->fopen,fwrite,fclose t%f sec.n", (nEnd-nStart)/nSec);}//end stdioWrite()void aioWrite(char * filename){struct aiocb aio;int outFile;struct timeval tvStart;struct timeval tvEnd;int64_t nEnd;int64_t nStart;gettimeofday(&tvStart);nStart = tvStart.tv_sec * 1000000 + tvStart.tv_usec;outFile = open(filename, O_WRONLY|O_CREAT, 0666);if(outFile == -1){fprintf(stderr, "[Error] Could not open %s for writing.n", filename);exit(1);}//end ifaio.aio_offset = 0;aio.aio_fildes = outFile;aio.aio_reqprio = 0;aio.aio_buf = pBytes;aio.aio_nbytes = strlen(pBytes);aio.aio_sigevent.sigev_notify = SIGEV_NONE;aio_write(&aio);while(aio_error(&aio) == EINPROGRESS);close(outFile);gettimeofday(&tvEnd);nEnd = tvEnd.tv_sec * 1000000 + tvEnd.tv_usec;nAioAvg += (nEnd-nStart);printf("aio->open,aio_write,close t%f sec.n", (nEnd-nStart)/nSec);}//end aioWrite()void genWrite(char * filename){int outFile;struct timeval tvStart;struct timeval tvEnd;int64_t nEnd;int64_t nStart;gettimeofday(&tvStart);nStart = tvStart.tv_sec * 1000000 + tvStart.tv_usec;outFile = open(filename, O_WRONLY|O_CREAT, 0666);if(outFile == -1){fprintf(stderr, "[Error] Could not open %s for writing.n", filename);exit(1);}//end ifwrite(outFile, pBytes, strlen(pBytes));close(outFile);gettimeofday(&tvEnd);nEnd = tvEnd.tv_sec * 1000000 + tvEnd.tv_usec;nGenAvg += (nEnd-nStart);printf("gen->open,write,close t%f sec.n", (nEnd-nStart)/nSec);}//end genWrite()void displayUsage(){printf("writetest - GodLikeMouse file write testing Version %d.%d.%dn", nVersionMajor, nVersionMinor, nVersionBuild);printf("tCopyright 2008 GodLikeMouse (www.GodLikeMouse.com)n");printf("n");printf("Usage:n");printf("tnqpcapd [options]n");printf("n");printf("Options:n");printf("t--output-dir [directory]n");printf("ttThe directory to write to for testing (default .test).n");printf("t--i [iterations]n");printf("ttThe amount of times to write (default 1).n");printf("t--mb [megabytes to write]n");printf("ttThe size of the files to write in megabytes.n");printf("t--b [bytes to write]n");printf("ttThe size of the files to write in bytes.n");printf("ttwritten (default /data).n");printf("t--stdion");printf("ttUse fopen,fwrite,fclose.n");printf("t--aion");printf("ttUse open,aio_write,close.n");printf("t--genion");printf("ttUse open,write,close.n");printf("t--helpn");printf("ttDisplay this help message.n");printf("t--versionn");printf("ttDisplay the version information.n");printf("n");}//end displayUsage()void parseArgs(int argc, char ** argv){int i;for(i=0; i<argc; i++){if(strstr(argv[i], "--output-dir")){sprintf(szOutputDir, "%s", argv[++i]);continue;}//end ifif(strstr(argv[i], "--mb")){nSize = mb * atol(argv[++i]);continue;}//end ifif(strstr(argv[i], "--b")){nSize = atol(argv[++i]);continue;}//end ifif(strstr(argv[i], "--help")){displayUsage();exit(0);}//end ifif(strstr(argv[i], "--i")){nIteration = atoi(argv[++i]);continue;}//end ifif(strstr(argv[i], "--aio")){nUseAio = 1;continue;}//end ifif(strstr(argv[i], "--stdio")){nUseStd = 1;continue;}//end ifif(strstr(argv[i], "--genio")){nUseGen = 1;continue;}//end ifif(strstr(argv[i], "--version")){printf("writetest - GodLikeMouse file write testing Version %d.%d.%dn", nVersionMajor, nVersionMinor, nVersionBuild);exit(0);}//end if}//end for}//end parseArgs()void printSeparator(){printf("---------------------------------------------n");}//end printSeparator()void printAverages(){double nTemp;if(nUseStd){nTemp = ((double)nStdioAvg/nIteration)/nSec;printf("stdio average write time: t%f sec.n", nTemp);printf("stdio average throughput: t%.0f bytes/sec ", nSize/nTemp);printf("%.0f MB/secn", (nSize/nTemp)/mb);}//end ifif(nUseAio){nTemp = ((double)nAioAvg/nIteration)/nSec;printf("aio average write time: t%f sec.n", nTemp);printf("aio average throughput: t%.0f bytes/sec ", nSize/nTemp);printf("%.0f MB/secn", (nSize/nTemp)/mb);}//end ifif(nUseGen){nTemp = ((double)nGenAvg/nIteration)/nSec;printf("gen average write time: t%f sec.n", nTemp);printf("gen average throughput: t%.0f bytes/sec ", nSize/nTemp);printf("%.0f MB/secn", (nSize/nTemp)/mb);}//end if}//end printAverages()int main(int argc, char ** argv){int i;char szFile[2048];nIteration = 1;nSize = 1024;strcpy(szOutputDir, ".test");nUseStd = 0;nUseAio = 0;nUseGen = 0;parseArgs(argc, argv);printf("n");printf("Beginning cycle writen");printf("Writing %ld bytes, %ld MBn", nSize, (nSize/mb));printSeparator();for(i=0; i<nIteration; i++){if(nUseStd){pBytes = (char *)malloc(nSize);memset(pBytes, 'X', nSize);sprintf(szFile, "%s/%s.%d", szOutputDir, "stdio", i);stdioWrite(szFile);free(pBytes);}//end ifif(nUseAio){pBytes = (char *)malloc(nSize);memset(pBytes, 'X', nSize);sprintf(szFile, "%s/%s.%d", szOutputDir, "aio", i);aioWrite(szFile);free(pBytes);}//end ifif(nUseGen){pBytes = (char *)malloc(nSize);memset(pBytes, 'X', nSize);sprintf(szFile, "%s/%s.%d", szOutputDir, "gen", i);genWrite(szFile);free(pBytes);}//end ifprintSeparator();}//end forprintf("n");printAverages();printf("n");printf("n");printf("Beginning sequential writen");printf("Writing %ld bytes, %ld MBn", nSize, (nSize/mb));printSeparator();nStdioAvg = 0;nAioAvg = 0;nGenAvg = 0;if(nUseStd){for(i=0; i<nIteration; i++){pBytes = (char *)malloc(nSize);memset(pBytes, 'X', nSize);sprintf(szFile, "%s/%s.%d", szOutputDir, "stdio", i);stdioWrite(szFile);free(pBytes);}//end forprintSeparator();}//end ifif(nUseAio){for(i=0; i<nIteration; i++){pBytes = (char *)malloc(nSize);memset(pBytes, 'X', nSize);sprintf(szFile, "%s/%s.%d", szOutputDir, "aio", i);aioWrite(szFile);free(pBytes);}//end forprintSeparator();}//end ifif(nUseGen){for(i=0; i<nIteration; i++){pBytes = (char *)malloc(nSize);memset(pBytes, 'X', nSize);sprintf(szFile, "%s/%s.%d", szOutputDir, "gen", i);genWrite(szFile);free(pBytes);}//end forprintSeparator();}//end ifprintf("n");printAverages();printf("n");}//end main() |
This simple program took in a set of parameters to determine which write methods to use to write, how much data, how many times and where to write it. Using this I began testing all the available free filesystems I could find for Linux. The fastest write speeds were given by XFS with the following make and mount options.
The first round metrics I received using this method to test are as follows:
Writing 500MB of data directly to disk using stdio (fopen,fwrite,fclose) aio (open,aio_write,close) and genio (open,write,close) for 3 iterations yeilded 456 when calling open,write,close consecutively; which is great, it meant I’m on the right track. After a few more tweaks and using genio (open,write,close) I started seeing:
Perfect, now I getting where I need to go and I know that XFS with the options I specified along with using the generic open,read,write approach would give me the best write times. Feel free to take the above writetest program and use it to tune your filesystem and to make sure that you’re using the fastest possible write method for your chosen filesystem. Be sure to compile with -laio. I thought these findings were worth mentioning.
**************** Update ********************
After changing the OS from a 32-bit to 64-bit system and with a few additional modifications to the kernel, new and even more impressive speeds have been reached.
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