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tomsk
Asked: 2017-03-05 13:34:56 +0800 CST

Check SSD's writes in some period

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I would like to install Ubuntu on SSD (I know that i Have to set TRIM, noatime, etc..) But I would like to know if I can check how many GB was written in last day / week / month.

Because I would like to measure how many GB is written every day on SSD if folders /var and /tmp were on SSD. If there would be less than 10GB writes per day I think it is cool and it will not damage SSD much.

And no I don't want to use ramdisk :)

ssd

1 Answers

  1. Best Answer

    As it often happens, I jumped ahead to reinvent the wheel that already exists in smartmontools package. This package provides whole lot of diagnostic tools for hard-drives and SSDs (or in more technical terms, SCSI devices). In particular, smartctl command is what we're looking for:

    $ sudo smartctl -A /dev/sda
[sudo] password for xieerqi: 
smartctl 6.5 2016-01-24 r4214 [x86_64-linux-4.4.0-65-generic] (local build)
Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF READ SMART DATA SECTION ===
SMART Attributes Data Structure revision number: 18
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Runtime_Bad_Block       0x0000   000   000   000    Old_age   Offline      -       0
  9 Power_On_Hours          0x0000   100   100   000    Old_age   Offline      -       8080
 12 Power_Cycle_Count       0x0000   100   100   000    Old_age   Offline      -       1419
171 Avail_OP_Block_Count    0x0000   100   100   000    Old_age   Offline      -       40907856
174 Pwr_Cycle_Ct_Unplanned  0x0000   100   100   000    Old_age   Offline      -       78
195 Total_Prog_Failures     0x0000   100   100   000    Old_age   Offline      -       0
196 Total_Erase_Failures    0x0000   100   100   000    Old_age   Offline      -       0
197 Total_Unc_Read_Failures 0x0000   100   100   000    Old_age   Offline      -       0
208 Average_Erase_Count     0x0000   100   100   000    Old_age   Offline      -       179
210 SATA_CRC_Error_Count    0x0000   100   100   000    Old_age   Offline      -       0
224 In_Warranty             0x0000   100   100   000    Old_age   Offline      -       1
233 Remaining_Lifetime_Perc 0x0000   095   095   000    Old_age   Offline      -       95
241 Host_Writes_GiB         0x0000   100   100   000    Old_age   Offline      -       3133
242 Host_Reads_GiB          0x0000   100   100   000    Old_age   Offline      -       2745
249 Total_NAND_Prog_Ct_GiB  0x0000   100   100   000    Old_age   Offline      -       301548705

    What you see above is list of attributes for my SSD. Of particular interest is attribute 241 (Host_Writes_GiB) and 242 (Host_Reads_GiB). These values are in GiB (which is a classical unit of measure in computer science in powers of 1024 bytes, in this case 1024^3, instead of SI units of powers of 10).

    On the low level, as far as I understand, this utility parses actual lifetime_write_kbytes file in /sys/fs folder. Particularly, in my example:

    $ cat /sys/fs/ext4/sda1/lifetime_write_kbytes              
4793857835

    Of course, this is a command-line utility. If you don't have it installed (check via apt-cache policy smartmontools) then install it via sudo apt-get install smartmontools. There is Gnome Disks Utility as GUI alternative and it comes with Ubuntu.

    There are couple caveats however:

    • SMART information has to be provided by the device. If the device is fairly cheap and doesn't have such information, then it would require reinventing the wheel just like I originally wanted to do via monitoring /proc/diskstats file.
    • The specific attributes must be provided by the device. For instance, information on tnfd22 ssd found on smartmontools website doesn't provide such information.

    There's also a bit of a problem: the resulting information shown is total history of reads/writes. Thus, you cannot extract reads/writes within last x number of days. At least it's not possible with smartctl or none of the tools I found thus far. However, what you can do, is schedule a daily cron task that will read /sys/fs/ext4/sda1/lifetime_write_kbytes and append the data with time stamp to a file. Later on, you can subtract differences to see how much was written in each day. For instance, contents of such command would be:

    30 08 * * * bash -c '{ date; cat /sys/fs/ext4/sda1/lifetime_write_kbytes; echo ;} >> /home/user/my_disk_log.txt'
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