Intel Server RAID Q1 2009 boot camp training lab workbook

Q1 2009 Intel

Server RAID Boot Camp Training

D: Impact of transfer block size on performance

Every data transfer request has a certain size. This size may be equal to the file size in case

of small files, or it may be equal to a database record size, or it may be hard-coded in an

application.

Examples:

- Typical database record size: 8KB-64KB

- Typical block size in data streaming applications: 256K – 4MB

- Typical block size used for transferring big files (file copy, FTP, HTTP): 64 KB

Transfer block size has great impact on performance. Also, the transfer block size is

coefficient between performance in terms of IOPS and performance (throughput) in terms of

MB/s. In case of constant transfer block size, the following formula is true:

Throughput (KB/s) = TransferBlockSize (KB) x Performance (IOPS)

Also, RAID performance depends on the relative sizes of the application transfer block and

RAID strip.

With sequential type of access, the transfer block size should be larger than stripe width

(strip size multiplied by the number of drives in the stripe) to get good performance

(throughput) in MB/s.

With random type of access, the transfer block size should be smaller than the strip size to

get good performance in IOPS.

1. On the Disk Targets tab set # of Outstanding I/Os = 1.

2. On the Access Specification tab make sure that 64KB Sequential Read is selected.

3. Click the Results Display tab, then click the Green Flag button to start the test and wait for 10

seconds for the test to complete.

4. Record the Total MBs per Second result into the MB/s column in the table below.

5. Repeat steps 2 through 4 with 8KB Sequential Read and with 1MB Sequential Read.

6. Compare the results.

Transfer Block Size MB/s

8 KB __________ MB/s

64 KB

_________ MB/s

1 MB

_________ MB/s

Questions

1. If we change 8 KB random read pattern to 16 KB random read, which performance metric

changes more – IOPS or MB/s?

2. If we change 1 MB sequential read pattern to 2 MB sequential read, which performance

metric changes more – IOPS or MB/s?

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