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Re: CF Card wear optimalisation for ext4



On Oct 8, 2014, at 10:28 AM, Jelle de Jong <jelledejong powercraft nl> wrote:
> Hello everyone,
> 
> I been using CF cards for almost more then 7 years now with ext
> file-system without any major problems on ALIX boards.
> 
> Last year I took 30 other systems in production with ext4 and the CF
> cards been dropping out pretty fast, it may have been a bad batch but
> I do want to look at it. I don't think the devices writes a lot of IO
> (is there a tool that can give me some useful numbers for say 24H or a
> week? iotop, atop, sysstat doesn?t seem suited for long term IO write
> monitoring, but maybe I am misusing them and can use some help here)

You can see in the ext4 superblock the amount of data that has been
written to a filesystem over its lifetime:

dumpe2fs -h /dev/vg_mookie/lv_home
dumpe2fs 1.42.7.wc2 (07-Nov-2013)
Filesystem volume name:   home
Last mounted on:          /home
:
:
Lifetime writes:          27 GB
:
:

Note that this number isn't wholly accurate, but rather a guideline.
IIRC it is not updated on disk all the time, so may lose writes.

You can also get this information from /sys/fs/ext4 including data
just for the current mount:

# grep . /sys/fs/ext4/*/*_write_kbytes 
/sys/fs/ext4/dm-0/lifetime_write_kbytes:77632360
/sys/fs/ext4/dm-0/session_write_kbytes:7124948
/sys/fs/ext4/dm-19/lifetime_write_kbytes:28081448
/sys/fs/ext4/dm-19/session_write_kbytes:16520
/sys/fs/ext4/dm-2/lifetime_write_kbytes:60847858
/sys/fs/ext4/dm-2/session_write_kbytes:7739388
/sys/fs/ext4/dm-7/lifetime_write_kbytes:22385952
/sys/fs/ext4/dm-7/session_write_kbytes:6379728
/sys/fs/ext4/sda1/lifetime_write_kbytes:835020
/sys/fs/ext4/sda1/session_write_kbytes:60848

> I mount root with the following options:
> 
> /dev/disk/by-uuid/09a04c01-64c6-4600-9e22-525667bda3e3 on / type ext4
> (rw,noatime,user_xattr,barrier=1,data=ordered)
> 
> # dumpe2fs /dev/sda1
> http://paste.debian.net/hidden/e3f81f11/
> 
> Are there kernel options to avoid synchronous disk writes? As
> suggested here: http://www.pcengines.ch/cfwear.htm

If you increase the journal commit interval (e.g. 30s) you can reduce
the number of times a block needs to be written to the journal.  The
drawback is that you also increase the amount of un-sync'd metadata
that would be lost in case of a crash.  This usually means the data
would also be lost, unless you are using a database-like workload that
overwrites the same files continuously.

> Is there a list of other kernel options I can optimise to limit any cf
> wear? The devices don't use
> 
> Kind regards
> 
> Jelle de Jong
> 
> 
> _______________________________________________
> Ext3-users mailing list
> Ext3-users redhat com
> https://www.redhat.com/mailman/listinfo/ext3-users


Cheers, Andreas





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