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Reader Comment: “DiskTester is awesome software as it detects irregularities before they become relevant”

DiskTester is part of diglloydTools. Read more about the capabilities of diglloydTools.

Gerrit V wrote MPG a few days ago:

I’m using disktester to check a striped array of two disks (raid-0) in my Mac Pro 2009. Both disks are HGST Ultrastore 7K3000 2TB and have run about 2month in a data center.

To my surprise DiskTester tells me about sluggish write values from time to time, see below in red:

DiskTester 2.2.5c 64-bit, diglloydTools 2.2.7b1, 2014-06-08 09:56
Copyright 2006-2014 DIGLLOYD INC. All Rights Reserved
Use of this software requires a license. See
OS X 10.11.1, 12 CPU cores, 16384MB memory
Samstag, 7. November 2015 um 14:13:19 Mitteleuropäische Normalzeit
disktester test-reliability —xfer 1M —iterations 3 Daten
TEMP FILE: /Volumes/Daten/disktester-test/DiskTester-Temporary-Test-File
Test size: 3.62TB
Free space untested: 22.3GB
Fill with: all
Testing reliability of volume „Daten“
Volume „Daten“: using 3.62TB test file, write/read/verify 1.50GB portions at a time using a 1MB memory buffer…
Begin iteration 1
427.5GB: 1.50GB/1MB (0)       152MB/sec … 152MB/sec
427.5GB: 1.50GB/1MB (1)       152MB/sec … 291MB/sec
427.5GB: 1.50GB/1MB (01)      150MB/sec … 186MB/sec
427.5GB: 1.50GB/1MB (10)      155MB/sec … 181MB/sec
427.5GB: 1.50GB/1MB (random)  148MB/sec … 184MB/sec
429GB: 1.50GB/1MB (0)       151MB/sec … 182MB/sec
429GB: 1.50GB/1MB (1)       151MB/sec … 290MB/sec
429GB: 1.50GB/1MB (01)      122MB/sec … 291MB/sec
429GB: 1.50GB/1MB (10)      150MB/sec … 182MB/sec
429GB: 1.50GB/1MB (random)  152MB/sec … 181MB/sec
430.5GB: 1.50GB/1MB (0)       152MB/sec … 286MB/sec
430.5GB: 1.50GB/1MB (1)       154MB/sec … 190MB/sec
430.5GB: 1.50GB/1MB (01)      152MB/sec … 181MB/sec
430.5GB: 1.50GB/1MB (10)      11.9MB/sec … 184MB/sec
430.5GB: 1.50GB/1MB (random)  150MB/sec … 256MB/sec
432GB: 1.50GB/1MB (0)       170MB/sec … 182MB/sec
432GB: 1.50GB/1MB (1)       164MB/sec … 182MB/sec
432GB: 1.50GB/1MB (01)      163MB/sec … 179MB/sec
432GB: 1.50GB/1MB (10)      162MB/sec … 292MB/sec
432GB: 1.50GB/1MB (random)  162MB/sec … 183MB/sec
433.5GB: 1.50GB/1MB (0)       151MB/sec … 181MB/sec
433.5GB: 1.50GB/1MB (1)       140MB/sec … 181MB/sec
433.5GB: 1.50GB/1MB (01)      151MB/sec … 178MB/sec
433.5GB: 1.50GB/1MB (10)      152MB/sec … 290MB/sec
433.5GB: 1.50GB/1MB (random)  153MB/sec … 182MB/sec
435GB: 1.50GB/1MB (0)       152MB/sec … 182MB/sec
435GB: 1.50GB/1MB (1)       150MB/sec … 181MB/sec
435GB: 1.50GB/1MB (01)      151MB/sec … 153MB/sec
435GB: 1.50GB/1MB (10)      153MB/sec … 179MB/sec
435GB: 1.50GB/1MB (random)  151MB/sec … 290MB/sec

MPG (Lloyd Chambers) replied in email as follows:

Any number of factors could cause such a delay, such as Spotlight trying to index something, an area of bad blocks, a new OS X glitch, etc.

If you break the RAID into two single drives / volumes, you can see if one drive has a performance issue. This can be done simultaneously in two Terminal windows, one invocation for each volume.

Gerrit responded today with:

I broke the RAID and ran the reliability test again on both drives. One went through without a glitch, but the other one stopped after a few GB. Now the controller doesn’t even recognize the drive.

Disktester really seems to be an awesome software as it detects irregularities before they become relevant.

Thank you very much for your support.

MPG recommends first using the DiskTester fill-volume command to graph performance of new drives before putting them into production use, and especially before putting them to use in a RAID (of any kind). Often there is a 10% or even 15% variance between same-model samples. Also useful for ferreting out sporadic problems is running DiskTester test-reliability.

For some brand SSDs, the DiskTester recondition SSD command can flush away performance issues.

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