{"id":95642,"date":"2024-08-28T06:00:00","date_gmt":"2024-08-28T11:00:00","guid":{"rendered":"https:\/\/eshop.macsales.com\/blog\/?p=95642"},"modified":"2024-09-03T23:54:53","modified_gmt":"2024-09-04T04:54:53","slug":"getting-the-most-performance-out-of-spinning-hard-drives-part-5-validating-hard-drive-performance-especially-for-raid","status":"publish","type":"post","link":"https:\/\/eshop.macsales.com\/blog\/95642-getting-the-most-performance-out-of-spinning-hard-drives-part-5-validating-hard-drive-performance-especially-for-raid\/","title":{"rendered":"Getting the Most Performance out of Spinning Hard Drives, Part 5: Validating Hard Drive Performance, Especially for RAID"},"content":{"rendered":"\n
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The Previous article in this series<\/a> discussed how to use 4 or 8 hard drives in a multi-drive enclosure, including RAID setups.<\/p>\n\n\n\n

When working with 4\/6\/8 hard drives at a time, there is a good chance that one of those drives will be a dud whose performance may on average<\/em> be similar but with oddball spikes of increased or decreased speed. Even by itself this is undesirable as it indicates a likely section of bad blacks that had to be mapped-out. High quality drives, particularly those for enterprise use, tend to have fewer such issues, but these can come at a stiff price premium.<\/p>\n\n\n\n

Matching performance in a RAID<\/h2>\n\n\n\n

Using different brands or even different drive models in a RAID is not a good plan due to differing performance behaviors: transfer rates, seek times, latency, etc. The rest of the discussion assumes matched drives.<\/p>\n\n\n\n

When used in a RAID, a variation of more than 4-5% in drive performance can significantly degrade RAID performance. With 3 or 4 or 7 of 8 drives having done their job, one laggard drive hangs up the entire transaction until it finishes\u2014transactions are gated by the slowest drive. Any drive that deviates too much should be replaced with one that performs consistently with all the others. <\/p>\n\n\n\n

There is no guarantee that any particular RAID vendor will detect this situation, since it requires a \u201cburn in\u201d period lasting 24 to 48 hours. In other words, it is costly to do so. But you can do it yourself.<\/p>\n\n\n\n

Example: Well-matched hard drives<\/h2>\n\n\n\n

Below, this graph shows shows four 22TB hard drives tested simultaneously. In this case, even though they are four different models and two different brands, they all perform similarly. <\/p>\n\n\n\n

However, the Seagate Iron Wolf Pro shows the highest read and write speeds by a little. Were I building a RAID, that\u2019s what I would pick for the best performance, though it would not matter all that much. Note also that the WD Pro Gold has noticeably slower speed (the yellow and blue lines). <\/p>\n\n\n\n

What you do not want to do is mix and match these drives<\/strong>, not just because of differeing transfer speeds, but because seek time and latency behavior might also differ, which could cause strange and unpredictable downward spikes in performance in a RAID.<\/p>\n\n\n\n

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Four 22TB hard drives tested over entire capacity<\/strong><\/figcaption><\/figure><\/div>\n\n\n\n

Example: One bad drive<\/h2>\n\n\n\n

The 6th drive crapped-out and could not complete the test, exhibiting erratic performance towards the end (orange line) utimately resulting in an I\/O error, which the SoftRAID driver also reported as a failure.<\/p>\n\n\n\n

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Six hard drives with one flaky one<\/strong><\/figcaption><\/figure><\/div>\n\n\n\n

DiskTester found the error:<\/p>\n\n\n\n

Task FileReaderTask exited with error: disk error (I\/O error) [-36]<\/strong>\nRead 523 files totaling 1.89TB in 13258.3 seconds @ 150MB\/sec\nNo verification failures<\/pre>\n\n\n\n
…and SoftRAID<\/a> (highly recommended) confirmed it:<\/p>\n\n\n\n
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SoftRAID Warning about bad sectors<\/figcaption><\/figure><\/div>\n\n\n\n
Testing the drives<\/h2>\n\n\n\n
As a rule, hard drives are not surface tested before being shipped. Bad drives can and do<\/em> get shipped.<\/p>\n\n\n\n
I am not aware of any tool that can emit data like that shown above other than my own diglloydTools DiskTester<\/a>. Its fill-volume command<\/a> writes 1000 files to fill the capacity of the drive. Benefits:<\/p>\n\n\n\n