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Developments for tape

Developments for tape

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Developments for tape

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  1. Developments for tape CASTOR workshop 2012 Author: Steven Murray (steven.murray@cern.ch)

  2. Contents • Immediate tape marks • Patching the SLC6 st driver • Configuring the bulk interface of tape • The solution to UNKNOWN tape drives • Virtual tape library - mhvtl Developments for tape - 2

  3. Before immediate tape marks 3 flushes per user file ≈ 5 seconds ≈ 1.2 GB that could have been written Drive scheduler VDQM 1. Mount tape 3. Write header file 4. Flush buffer 5. Write user file 6. Flush buffer 7. Write trailer file 8. Flush buffer 2. File info Legacy tape transfer-manager RTCPCLIENTD Legacy tape reader/writer RTCPD 9. Wrote file Developments for tape - 3

  4. What is an immediate tape mark • Synchronous tape mark - Mark the end of file and flush struct mtop mtop; mtop.mt_op = MTWEOF; mtop.mt_count = 1; ioctl(tapefd, MTIOCTOP, &mtop); • Immediate tape mark – Just mark the end of file; no flush struct mtop mtop; mtop.mt_op = MTWEOFI; mtop.mt_count = 1; ioctl(tapefd, MTIOCTOP, &mtop); • Flush tape drive buffer - Flush struct mtop mtop; mtop.mt_op = MTWEOF; mtop.mt_count = 0; ioctl(tapefd, MTIOCTOP, &mtop); Developments for tape - 4

  5. After immediate tape marks Tape format has not been changed! Drive scheduler VDQM 1. Mount tape Drive buffer flushed less often Bulk protocol 2. File info for N files Tape gateway Protocol bridge For N files or data loop 3. Write header file 4. Write user file 5. Write trailer file End loop 6. Flush buffer 7. Wrote N files Legacy tape transfer-manager RTCPCLIENTD Legacy tape reader/writer RTCPD Developments for tape - 5

  6. Results of immediate tape marks Developments for tape - 6

  7. SLC5 st driver has 2 patches • MTWEOFI • Provides support for immediate tape marks • CASTOR cannot run without it • MTIOCSENSE • Improves error diagnosis • CASTOR can run without it. Developments for tape - 7

  8. SLC6 st driver has 1 patch • The SLC6 st driver currently has the MTWEOFI patch • The SLC6 st driver is used by virtual tape servers • Real hardware will decide whether or not we require the MTIOCSENSE patch Developments for tape - 8

  9. Tape bulk-interface configuration • TAPEBRIDGE BULKREQUESTMIGRATIONMAXBYTES • The maximum number of bytes a set of files to migrate should represent • TAPEBRIDGE BULKREQUESTMIGRATIONMAXFILES • The maximum number of files in a migration set • TAPEBRIDGE BULKREQUESTRECALLMAXBYTES • The maximum number of bytes a set of files to recall should represent • TAPEBRIDGE BULKREQUESTRECALLMAXFILES • The maximum number of files in a recall set Developments for tape - 9

  10. UNKNOWN tape drives fixed • Drives stuck in UNKNOWN in the VDQM • Operator had to manually DOWN and UP drives • After 5 years bug was tracked to the new VDQM • Race condition between an unused monitoring message and a state change message • Race condition removed in 2.1.13-6 tape servers Developments for tape - 10

  11. Architecture of mhvtl rtcpd daemon rmcd daemon vtltape daemon vtllibrary daemon User Space Kernel space st driver sg driver SCSI mid-layer mhvtl driver (pseudo host bus adapter - HBA) Developments for tape - 11

  12. mhvtl configuration and data files • Configuration files are in /etc/mhvtl • device.conf • Specifies the tape library and drive devices • mhvtl.conf • Default media capacity • syslog verbosity of the vtltape and vtllibrary daemons • Kernel module debugging level • Data files are in /opt/mhvtl • One directory per tape Developments for tape - 12

  13. rpms of mhvtl • Available from the Enterprse Linux Repository • SLC5 rpms • mhvtl-utils-1.4.4-1.el5.elrepo • User-space daemons and clients • kmod-mhvtl-1.4.4-1.el5.elrepo • Kernel module • SLC6 rpms • mhvtl-utils-1.4.4-1.el6.elrepo.x86_64.rpm • kmod-mhvtl-1.4.4-1.el6.elrepo.x86_64.rpm Developments for tape - 13

  14. mhvtl compression statistics • Victor Kotlyar helped fix the mhvtl compression statics • LOG SELECT: Fix off-by-one issues • https://github.com/markh794/mhvtl/commit/07d9bc4852da0d59fcdec70c3168d3e96f9226a8 • Implement Parameter Code Reset in LOG SELECT • https://github.com/markh794/mhvtl/commit/335785b493430323e4dbaacc0c89fe78b425a5db • mhvtl-1.4.4 was created by Mark Harvey (MH vtl). • Thanks to contact withdag@wieers.com this new version was built in general ELRepo (Enterprse Linux Repository). Developments for tape - 14