Pending Inconsistent results between sub-block options (/3, /4, etc)

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ColbyBouma

Well-known member
Dec 26, 2020
132
54
I stumbled across this while messing around with a drive I got recently (the Kingston below). I noticed that its /4 results were noticeably higher than its regular results. I tested a few more drives and discovered that they're the opposite. Most drives get slower with the higher options. I ran each test multiple times and calculated the average. I attached all of the logs below.

Crucial BX100
Sub-block level0%25%50%75%100%
0516.6542.1542.2542.1542.0
1516.6542.1542.2542.1542.0
2516.2541.8541.9541.8541.8
3514.3541.5541.7541.5541.5
4510.2540.6541.0540.6540.8

Kingston SA400M8120G
Sub-block level0%25%50%75%100%
0294.3281.2280.8281.3287.4
1294.3281.2280.8281.3287.5
2293.2281.7280.9282.1286.8
3291.7282.7281.3283.3285.4
4306.4300.2297.6301.2300.0

KingDian S100
Sub-block level0%25%50%75%100%
0193.3194.5190.5189.5189.3
1193.3194.5190.5189.5189.3
2193.1194.4190.4189.4189.2
3192.8194.2190.2189.2188.9
4192.0193.5189.6188.6188.2

Intel SSDSA2M080G2HP
Sub-block level0%25%50%75%100%
0250.5261.2264.5262.3265.2
1250.5261.4264.4262.3265.2
2249.4260.5261.7261.0264.1
3247.3257.8258.8253.7262.2
4242.4248.9254.9244.0258.0
 

Attachments

  • Sub-block Testing.zip
    156.7 KB · Views: 282
SSDs are quite complex and data from a large read may be actually spread over several chips which can be accessed in parallel, in a RAID like manner. That's just one possible explanation I can quickly think of. So big chunk can be read from several chips in parallel > more data p/s > better benchmark.

Also, as 'chunk' size increases what also may come into play is handling of errors. More data you read at once, the bigger chance the drive has to handle an error, for example employing ECC correction. If we assume 1 MB data occupying 3 cells that need ECC correction, of several small chunk reads will not encounter error while only a few will, 'upping' average, reading data in 4 chunks while 3 need to wait for ECC correction may affect average in benchmark. I guess depending on properties of NAND chips, how well firmware is optimized, buffer size etc. you may find different tipping points.

Just thinking out loud, not pretending to be giving definitive answers.