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Results
The following tables indicate the results of our test runs. Note that each table contains results for tests run on two varieties of 4.2BSD file systems. The first set of results is always for a file system with a basic blocking factor of eight Kilobytes and a fragment size of 1 Kilobyte. The second sets of measurements are for file systems with a four Kilobyte block size and a one Kilobyte fragment size. The values in parenthesis indicate the percentage of CPU time used by the test program. In the case of the two disk arm tests, the value in parenthesis indicates the sum of the percentage of the test programs that were run. Entries of ``n. m.'' indicate this value was not measured.
| 4.2BSD File Systems Tests - VAX 11/750 |
| Logically Sequential Transfers |
| from an 8K/1K 4.2BSD File System (Kbytes/sec.) |
| Test Emulex SC750/Eagle UDA50/RA81 |
| 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 490 (69%) 620 (96%) 310 (44%) 520 (65%) |
| write_4096 380 (99%) 370 (99%) 370 (97%) 360 (98%) |
| write_8192 470 (99%) 470 (99%) 320 (71%) 410 (83%) |
| rewrite_8192 650 (99%) 620 (99%) 310 (50%) 450 (70%) |
| .T& |
| c s s s s |
| c s s s s |
| l | l s | l s |
| l | l s | l s |
| l | l l | l l |
| l | c c | c c. |
| Logically Sequential Transfers |
| from 4K/1K 4.2BSD File System (Kbytes/sec.) |
| Test Emulex SC750/Eagle UDA50/RA81 |
| 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 300 (60%) 400 (84%) 210 (42%) 340 (77%) |
| write_4096 320 (98%) 320 (98%) 220 (67%) 290 (99%) |
| write_8192 340 (98%) 340 (99%) 220 (65%) 310 (98%) |
| rewrite_8192 450 (99%) 450 (98%) 230 (47%) 340 (78%) |
Note that the rate of write operations on the VAX 11/750 are ultimately CPU limited in some cases. The write rates saturate the CPU at a lower bandwidth than the reads because they must do disk allocation in addition to moving the data from the user program to the disk. The UDA50/RA81 saturates the CPU at a lower transfer rate for a given operation than the SC750/Eagle because it causes more memory contention with the CPU. We do not know if this contention is caused by the UNIBUS controller or the UDA50.
The following table reports the results of test runs on a VAX 11/780 with 4 Megabytes of main memory.
| 4.2BSD File Systems Tests - VAX 11/780 |
| Logically Sequential Transfers |
| from an 8K/1K 4.2BSD File System (Kbytes/sec.) |
| Test Emulex SC780/Eagle UDA50/RA81 Sys. Ind. 9900/Eagle |
| 1 Drive 2 Drives 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 560 (70%) 480 (58%) 360 (45%) 540 (72%) 340 (41%) 520 (66%) |
| write_4096 440 (98%) 440 (98%) 380 (99%) 480 (96%) 490 (96%) 440 (84%) |
| write_8192 490 (98%) 490 (98%) 220 (58%)* 480 (92%) 490 (80%) 430 (72%) |
| rewrite_8192 760 (100%) 560 (72%) 220 (50%)* 180 (52%)* 490 (60%) 520 (62%) |
| .T& |
| c s s s s s s |
| c s s s s s s |
| l | l s | l s | l s |
| l | l s | l s | l s |
| l | l l | l l | l l |
| l | c c | c c | c c. |
| Logically Sequential Transfers |
| from an 4K/1K 4.2BSD File System (Kbytes/sec.) |
| Test Emulex SC780/Eagle UDA50/RA81 Sys. Ind. 9900/Eagle |
| 1 Drive 2 Drives 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 490 (77%) 370 (66%) n.m. n.m. 200 (31%) 370 (56%) |
| write_4096 380 (98%) 370 (98%) n.m. n.m. 200 (46%) 370 (88%) |
| write_8192 380 (99%) 370 (97%) n.m. n.m. 200 (45%) 320 (76%) |
| rewrite_8192 490 (87%) 350 (66%) n.m. n.m. 200 (31%) 300 (46%) |
The dropoff in reading and writing rates for the two drive SC780/Eagle tests are probably due to the file system using insufficient rotational delay for these tests. We have not fully investigated these times.
The following table compares data rates on VAX 11/750s directly with those of VAX 11/780s using the UDA50/RA81 storage system.
| 4.2BSD File Systems Tests - DEC UDA50 - 750 vs. 780 |
| Logically Sequential Transfers |
| from an 8K/1K 4.2BSD File System (Kbytes/sec.) |
| Test VAX 11/750 UNIBUS VAX 11/780 UNIBUS |
| 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 310 (44%) 520 (84%) 360 (45%) 540 (72%) |
| write_4096 370 (97%) 360 (100%) 380 (99%) 480 (96%) |
| write_8192 320 (71%) 410 (96%) 220 (58%)* 480 (92%) |
| rewrite_8192 310 (50%) 450 (80%) 220 (50%)* 180 (52%)* |
| .T& |
| c s s s s |
| c s s s s |
| l | l s | l s |
| l | l s | l s |
| l | l l | l l |
| l | c c | c c. |
| Logically Sequential Transfers |
| from an 4K/1K 4.2BSD File System (Kbytes/sec.) |
| Test VAX 11/750 UNIBUS VAX 11/780 UNIBUS |
| 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 210 (42%) 342 (77%) n.m. n.m. |
| write_4096 215 (67%) 294 (99%) n.m. n.m. |
| write_8192 215 (65%) 305 (98%) n.m. n.m. |
| rewrite_8192 227 (47%) 336 (78%) n.m. n.m. |
The higher throughput available on VAX 11/780s is due to a number of factors. The larger main memory size allows a larger file system cache. The block allocation routines run faster, raising the upper limit on the data rates in writing new files.
The next table makes the same comparison using an Emulex controller on both systems.
| 4.2BSD File Systems Tests - Emulex - 750 vs. 780 |
| Logically Sequential Transfers |
| from an 8K/1K 4.2BSD File System (Kbytes/sec.) |
| Test VAX 11/750 CMI Bus VAX 11/780 SBI Bus |
| 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 490 (69%) 620 (96%) 560 (70%) 480 (58%) |
| write_4096 380 (99%) 370 (99%) 440 (98%) 440 (98%) |
| write_8192 470 (99%) 470 (99%) 490 (98%) 490 (98%) |
| rewrite_8192 650 (99%) 620 (99%) 760 (100%) 560 (72%) |
| .T& |
| c s s s s |
| c s s s s |
| l | l s | l s |
| l | l s | l s |
| l | l l | l l |
| l | c c | c c. |
| Logically Sequential Transfers |
| from an 4K/1K 4.2BSD File System (Kbytes/sec.) |
| Test VAX 11/750 CMI Bus VAX 11/780 SBI Bus |
| 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 300 (60%) 400 (84%) 490 (77%) 370 (66%) |
| write_4096 320 (98%) 320 (98%) 380 (98%) 370 (98%) |
| write_8192 340 (98%) 340 (99%) 380 (99%) 370 (97%) |
| rewrite_8192 450 (99%) 450 (98%) 490 (87%) 350 (66%) |
The following table illustrates the evolution of our testing process as both hardware and software problems effecting the performance of the Emulex SC780 were corrected. The software change was suggested to us by George Goble of Purdue University.
The 4.2BSD handler for RH750/RH780 interfaced disk drives contains several constants which to determine how much time is provided between an interrupt signaling the completion of a positioning command and the subsequent start of a data transfer operation. These lead times are expressed as sectors of rotational delay. If they are too small, an extra complete rotation will often be required between a seek and subsequent read or write operation. The higher bit rate and rotational speed of the 2351A Fujitsu disk drives required increasing these constants.
The hardware change involved allowing for slightly longer delays in arbitrating for cycles on the SBI bus by starting the bus arbitration cycle a little further ahead of when the data was ready for transfer. Finally we had to increase the rotational delay between consecutive blocks in the file because the higher bandwidth from the disk generated more memory contention, which slowed down the processor.
| 4.2BSD File Systems Tests - Emulex SC780 Disk Controller Evolution |
| Logically Sequential Transfers |
| from an 8K/1K 4.2BSD File System (Kbytes/sec.) |
| Test Inadequate Search Lead OK Search Lead OK Search Lead |
| Initial SBI Arbitration Init SBI Arb. Improved SBI Arb. |
| 1 Drive 2 Drives 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 320 370 440 (60%) n.m. 560 (70%) 480 (58%) |
| write_4096 250 270 300 (63%) n.m. 440 (98%) 440 (98%) |
| write_8192 250 280 340 (60%) n.m. 490 (98%) 490 (98%) |
| rewrite_8192 250 290 380 (48%) n.m. 760 (100%) 560 (72%) |
| .T& |
| c s s s s s s |
| c s s s s s s |
| l | l s | l s | l s |
| l | l s | l s | l s |
| l | l s | l s | l s |
| l | c c | c c | c c |
| l | c c | c c | c c. |
| Logically Sequential Transfers |
| from an 4K/1K 4.2BSD File System (Kbytes/sec.) |
| Test Inadequate Search Lead OK Search Lead OK Search Lead |
| Initial SBI Arbitration Init SBI Arb. Improved SBI Arb. |
| 1 Drive 2 Drives 1 Drive 2 Drives 1 Drive 2 Drives |
| read_8192 200 220 280 n.m. 490 (77%) 370 (66%) |
| write_4096 180 190 300 n.m. 380 (98%) 370 (98%) |
| write_8192 180 200 320 n.m. 380 (99%) 370 (97%) |
| rewrite_8192 190 200 340 n.m. 490 (87%) 350 (66%) |