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Linux IOzone Workload

To do disk performance studies, we often use a Linux guest running the tool IOzone. IOzone is a publicly available disk performance analyzer. It runs on a number of platforms. See iozone.org for more information.

IOzone is a straightforward file system exerciser that measures disk performance through the following four-phase experiment:

  1. It creates a new file and writes it from beginning to end;
  2. It rewrites the file;
  3. It reads the file it just wrote;
  4. It rereads the file it just wrote.

Each of the four phases operates on the file in an interlaced fashion. By interlaced we mean that the file is not just sequentially handled from beginning to end. Rather, IOzone uses an input parameter called the stride to handle a record, skip over many records, handle another record, skip again, and so on, proceeding in modulus fashion until all records have been handled. For example, during the write pass, if the stride were set to 17 records, IOzone would write records 0, 17, 34, 51, ..., 1, 18, 35, ..., and so on until all records were written.

IOzone measures the elapsed time it experiences during each of the four phases of its experiment and prints the KB-per-second data rate it experiences in each phase.

To collect processor time per transaction, we use the zSeries hardware sampler to measure processor time. We define a transaction to be 100 KB handled through the four phases of the IOzone run. In other words, we define that the run contains 8192 transactions.

We run IOzone as follows:

  • Linux guest virtual machine size is 192 MB.
  • Linux file system is ext2.
  • Ballast file 800 MB.
  • Record size 64 KB.
  • Processor cache size set to 1024 Kbytes.
  • Processor cache line size set to 256 bytes.
  • File stride size set to 17 * record size.
  • Throughput test with 1 process.
  • Include fsync in write timing.

It is important to notice that we chose the ballast file to be about four times larger than the virtual machine. This ensures that the Linux page cache plays little to no role in buffering IOzone's file operations. We wanted to be sure to measure disk I/O performance, not the performance of the Linux page cache.

We measure several different choices for disk technology, as described in the following table. The abbreviations explained in the table below appear elsewhere in this report as shorthand so as to describe the configurations measured.

Regarding block size, the following notes apply:

  • For mke2fs, we use block sizes (-bs parameter) of 1024, 2048, or 4096 bytes, as called out in the tables below.
  • On ECKD DASD, the formatting of the DASD tracks matches the -bs setting we use in mke2fs.
  • On FBA DASD, the volumes are always formatted at 512 bytes per block.

Run Subsystem Disk type Attachment MDC setting Linux driver Block size
EDED 2105-F20 FICON ECKD Dedicated n/a ECKD SSCH 4096
EMD0 2105-F20 FICON ECKD Minidisk OFF ECKD SSCH 4096
EMD1 2105-F20 FICON ECKD Minidisk ON ECKD SSCH 4096
FDED 2105-F20 FCP Emulated FBA Dedicated n/a FBA SSCH 4096
FMD0 2105-F20 FCP Emulated FBA Minidisk OFF FBA SSCH 4096
FMD1 2105-F20 FCP Emulated FBA Minidisk ON FBA SSCH 4096
9DED FAStT900 FCP with EDEV attribute FASTT Emulated FBA Dedicated n/a FBA SSCH 4096
9MD0 FAStT900 FCP with EDEV attribute FASTT Emulated FBA Minidisk OFF FBA SSCH 4096
9MD1 FAStT900 FCP with EDEV attribute FASTT Emulated FBA Minidisk ON FBA SSCH 4096
LNS0 2105-F20 FCP SCSI Linux owns FCP adapter subchannel n/a zFCP 4096
D210 2105-F20 FICON ECKD Minidisk OFF Diag X'250' 1024
D211 2105-F20 FICON ECKD Minidisk ON Diag X'250' 1024
D220 2105-F20 FICON ECKD Minidisk OFF Diag X'250' 2048
D221 2105-F20 FICON ECKD Minidisk ON Diag X'250' 2048
D240 2105-F20 FICON ECKD Minidisk OFF Diag X'250' 4096
D241 2105-F20 FICON ECKD Minidisk ON Diag X'250' 4096
G210 2105-F20 FCP Emulated FBA Minidisk OFF Diag X'250' 1024
G211 2105-F20 FCP Emulated FBA Minidisk ON Diag X'250' 1024
G220 2105-F20 FCP Emulated FBA Minidisk OFF Diag X'250' 2048
G221 2105-F20 FCP Emulated FBA Minidisk ON Diag X'250' 2048
G240 2105-F20 FCP Emulated FBA Minidisk OFF Diag X'250' 4096
G241 2105-F20 FCP Emulated FBA Minidisk ON Diag X'250' 4096

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