On Thu, Sep 12, 2013 at 10:54:03AM -0400, Calvin Walton wrote: > On Thu, 2013-09-12 at 16:18 +0200, Julian Andres Klode wrote: > > Hi, > > > > I installed my new laptop on Saturday and setup an ext4 filesystem > > on my / and /home partitions. Without me doing much file transfers, > > I noticed today: > > > > jak@jak-x230:~$ cat /sys/fs/ext4/sdb3/lifetime_write_kbytes > > 342614039 > > > > This is on a 100GB partition. I used fstrim multiple times. I analysed > > the increase over some time today and issued an fstrim in between: > <snip> > > So it seems that ext4 counts the trims as writes? I don't know how I could > > get 300GB of writes on a 100GB partition -- of which only 8 GB are occupied > > -- otherwise. > > The way fstrim works is that it allocates a temporary file that fills > almost the entire free space on the partition. I believe it does this > with fallocate in order to ensure that space for the file is actually > reserved on disc (but it does not get written to!). It then looks up > where on disc the file's reserved space is, and sends a trim command to > the drive to free that space. Afterwards, it deletes the temporary file. > > So what you are seeing means means that it's probably just an issue with > the write accounting, where the blocks reserved by the fallocate are > counted as writes. I can also confirm that using fallocate to allocate a 1G file (and deleting it afterwards without modifying it in between; with discard enabled [I enabled this now after the log for testing]) also increases the write number by 1G. > > > My smart values for my SSD are: > > > > SMART Attributes Data Structure revision number: 1 > > Vendor Specific SMART Attributes with Thresholds: > > ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE > > 241 Total_LBAs_Written 0x0003 100 100 000 Pre-fail Always - 1494 > > You should be able to confirm this by checking the 'Total_LBAs_Written' > attribute before and after doing the fstrim; it should either not go up, > or go up only be a small amount. Although to be honest, I'm not sure > what this is counting - if that raw value is actually LBAs, that would > only account for 747KiB of writes! I guess it's probably a count of > erase blocks or something - what model is the SSD? It was 1493 some time before the trim. The disk is a PLEXTOR PX-128M5. -- Julian Andres Klode - Debian Developer, Ubuntu Member See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
