Re: Home Directory in SSD

[Martin Steigerwald <martin@lichtvoll.de>]

Am Sonntag, 7. Februar 2016, 08:48:55 CET schrieb Jos Collin:
> Hi,

Hi Jos,

> First of all, I apologize for starting an off-topic discussion.
> 
> i'm using an Intel 535 Series 120GB SSD. So I believe that it is
> reliable and good quality product.

I am very pleased with my Intel SSD 320 and back then only Intel published a 
statistic on failure rates. It was about 0,6% of devices being sent back (I 
think X-25M still back then) and about 0,4% of devices being actually really 
faulty. I didn´t have exact figures of other vendors but I think at least for 
some of them back then it has been more like 2-3% of device failures.

Now 0,4 is still one device out of 1000 failing.

I am not sure about the current state of affairs, but I do think Intel 
generally does reliable SSDs. Maybe not always the fastest ones,  but honestly 
I don´t care that much. If its more reliable I tolerate a bit lower 
performance. Of course it shouldn´t crawl down on write access.

> I have installed the entire OS in the SSD now. But considering the
> failure rate of all SSDs in common, I'm thinking of creating a partition
> for /home in the HDD and mount it during boot. But as I have already
> created /home in the SSD, I have to move that to the new partition in
> HDD now. I can leave /root in the SSD itself, as suggested by Matus
> UHLAR in the other email thread. This method will secure the user data
> on the fly, even though there is a compromise in performance (not a big
> deal).

If you have both an SSD and a HD in your machine, how about rsync or BTRFS 
send and receive to regularily backup /home from SSD to HD?

With BTRFS on the HD, you can even snapshot your backup states and if you 
accidentally delete a file get it back from a backup. I think I´d use it if 
that laptop would still have an SSD.

Right now I use BTRFS RAID 1 on two SSDs for important data like the data in /
home:

merkaba:~#1> btrfs scrub status -d /home
scrub status for […]
scrub device /dev/dm-0 (id 1) history
        scrub started at Sat Feb  6 17:56:55 2016 and finished after 00:10:08
        total bytes scrubbed: 152.88GiB with 0 errors
scrub device /dev/mapper/sata-home (id 2) history
        scrub started at Sat Feb  6 17:56:55 2016 and finished after 00:11:09
        total bytes scrubbed: 152.88GiB with 0 errors

merkaba:~> btrfs device stats /home
[/dev/mapper/msata-home].write_io_errs   0
[/dev/mapper/msata-home].read_io_errs    0
[/dev/mapper/msata-home].flush_io_errs   0
[/dev/mapper/msata-home].corruption_errs 0
[/dev/mapper/msata-home].generation_errs 0
[/dev/mapper/sata-home].write_io_errs   0
[/dev/mapper/sata-home].read_io_errs    0
[/dev/mapper/sata-home].flush_io_errs   0
[/dev/mapper/sata-home].corruption_errs 0
[/dev/mapper/sata-home].generation_errs 0

I really like it that BTRFS can basically prove to me that the data is okay. 
So I also use it on my 2 TB backup harddisk, where I use its snapshot 
functionality to keep old backup states as well. I still use rsync for backup, 
but I consider switching to btrfs send/receive after testing it maybe with the 
smaller / (in addition to rsync) for a while.


Remembers me to scrub / and /daten (for larger files only on the larger SSD) 
as well again. :)

Thanks,
-- 
Martin