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fgrieu
Asked: 2019-11-22 00:58:58 +0800 CST

Unit for Total_LBAs_Written in SMART data

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I have 3 machines with disks (actually, SSDs) in RAID1, purposely with different brands in an attempt to make it improbable to loose them both simultaneously due to wear-out. They are functional.

They should have approximately the same number of Total_LBAs_Written on their two disks. But the figure are wildly different, e.g. smartctl reports 2596016156 on a Samsung SSD 850 EVO 2TB, but 1237 on the companion WDC WDS200T2B0A-00SM50:

241  Total_LBAs_Written  0x0032  099 099 000  Old_age  Always   -  2596016156
241  Total_LBAs_Written  0x0030  253 253 ---  Old_age  Offline  -  1237

My best guess is that the first report is in blocks of 512 bytes, and the second in Gibibyte. That would explain that the ratio is 221 (within one unit for the smaller value).

Is the unit for the Total_LBAs_Written entry standardized somewhere? Is there a systematic way to determine it? If not, what units are practiced?

hard-drive

1 Answers

  1. I think your guess is right. I have a HooDisk SSD 128G, and made the following test:

    1. read atribute: 289
    2. write 1G of data
    3. read atribute: 290
    4. write 1G of data
    5. read atribute: 291

    comands:

    $ smartctl -a /dev/sda |awk '/Total_LBAs_Written/ {print $10}'
289
$ dd if=/dev/zero of=/home/testimage bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 3.54747 s, 303 MB/s
$ smartctl -a /dev/sda |awk '/Total_LBAs_Written/ {print $10}'
290
$ dd if=/dev/zero of=/home/testimage bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 3.42046 s, 314 MB/s
$ smartctl -a /dev/sda |awk '/Total_LBAs_Written/ {print $10}'
291
$

    based on wikipedia: https://en.wikipedia.org/wiki/S.M.A.R.T.#Known_ATA_S.M.A.R.T._attributes It didn't say about the unit of this attribute, so I guess its not well standarized, you'd better to specifictly test the device to determine its meanings.

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