HP-UX VxFS tuning and performance - filibeto.org

More documents

Recommendations

Info

16 Figure 10. Locking with concurrent I/O (cio) To enable a file system for concurrent I/O, the file system simply needs to be mounted with the cio mount option, for example: # mount -F vxfs -o cio,delaylog /dev/vgora5/lvol1 /oracledb/s05 Concurrent I/O was introduced with VxFS 3.5. However, a separate license was needed to enable concurrent I/O. With the introduction of VxFS 5.0.1 on HP-UX 11i v3, the concurrent I/O feature of VxFS is now available with the OnlineJFS license. While concurrent I/O sounds like a great solution to alleviate VxFS inode lock contention, and it is, some major caveats exist that anyone who plans to use concurrent I/O should be aware of. Concurrent I/O converts read and write operations to direct I/O Some applications benefit greatly from the use of cached I/O, relying on cache hits to reduce the amount of physical I/O or VxFS read ahead to prefetch data and reduce the read time. Concurrent I/O converts most read and write operations to direct I/O, which bypasses the buffer/file cache. If a file system is mounted with the cio mount option, then mount options mincache=direct and convosync=direct are implied. If the mincache=direct and convosync=direct options are used, they should have no impact if the cio option is used as well. Since concurrent I/O converts read and write operations to direct I/O, all alignment constraints for direct I/O also apply to concurrent I/O. Certain operations still take exclusive locks Some operations still need to take an exclusive lock when performing I/O and can negate the impact of concurrent I/O. The following is a list of operations that still need to obtain an exclusive lock. 1. fsync() 2. writes that span multiple file extents 3. writes when request is not aligned on a 1 KB boundary 4. extending writes 5. allocating writes to “holes” in a sparse file 6. writes to Zero Filled On Demand (ZFOD) extents
Zero Filled On Demand (ZFOD) extents are new with VxFS 5.0 and are created by the VX_SETEXT ioctl() with the VX_GROWFILE allocation flag, or with setext(1M) growfile option. Not all applications support concurrent I/O By using a shared lock for write operations, concurrent I/O breaks some POSIX standards. If two processes are writing to the same block, there is no coordination between the files, and data modified by one process can be lost by data modified by another process. Before implementing concurrent I/O, the application vendors should be consulted to be sure concurrent I/O is supported with the application. Performance improvements with concurrent I/O vary Concurrent I/O benefits performance the most when there are multiple processes reading a single file and one or more processes writing to the same file. The more writes performed to a file with multiple readers, the greater the VxFS inode lock contention and the more likely that concurrent I/O will benefit. A file system must be un-mounted to remove the cio mount option A file system may be remounted with the cio mount option ("mount -o remount,cio /fs"); however to remove the cio option, the file system must be completely unmounted using umount(1M). Oracle Disk Manager Oracle Disk Manager (ODM) is an additionally licensed feature specifically for use with Oracle database environments. If the oracle binary is linked with the ODM library, Oracle will make an ioctl() call to the ODM driver to initiate multiple I/O requests. The I/O requests will be issued in parallel and will be asynchronous provided the disk_asynch_io value is set to 1 in the init.ora file. Later, Oracle will make another ioctl() call to process the I/O completions. Figure 11. Locking with concurrent I/O (cio) ODM provides near raw device asynchronous I/O access. It also eliminates the VxFS inode lock contention (similar to concurrent I/O). 17
Page 1 and 2: HP-UX VxFS tuning and performance T
Page 3 and 4: Understanding VxFS In order to full
Page 5 and 6: File system reorganization attempts
Page 7 and 8: Read ahead with VxVM stripes The de
Page 9 and 10: Figure 4. Flush behind As data is w
Page 11 and 12: The read flush behind feature has t
Page 13 and 14: Note The OnlineJFS license is requi
Page 15: Concurrent I/O The main problem add
Page 19 and 20: Table 3. Default intent log size FS
Page 21 and 22: Using datainlog has no affect on no
Page 23 and 24: Table 4. Intent log flush behavior
Page 25 and 26: ead_ahead The default read_ahead va
Page 27 and 28: Unified File Cache on HP-UX 11i v3
Page 29 and 30: Note When setting vx_ninode to redu
Page 31 and 32: Patches Performance problems are of

HP-UX VxFS tuning and performance - filibeto.org

Create successful ePaper yourself

Delete template?

Save as template?