[mythtv-users] Mirroring root partition on SSD to a hard drive -- bad idea?

digid myth digidmyth at gmail.com
Fri Jan 15 02:20:08 UTC 2016


Here are some of my thoughts.

Currently I have two SSD's in raid 1 for my OS filesystem on my Myth Box.
This server is a general purpose server, so does a lot more work than just
Myth TV.

I have had SSD's fail but they were older SSD's and in all cases were tight
on space. For this server I chose to use larger SSD's with the idea that
the TRIM would level out the writes over more the the SSD and add to its
life. I currently am using 250 Gig SSD's for the os. They are set up as 1
large partition.  I have turned on all of the SSD features in Linux. I do
have a separate 1 TB drive for recordings two 4tb drives for Videos as well
as a pair of 2 TB drives in raid 1 for my general data share.

I do not like the idea of making a backup of the whole drive with the cp
command. By moving all of you files you are forcing a read on every
allocated sector, and a write on every allocated sector on the destination
drive. This is time-consuming and hard on the drive.

My normal routine on my servers is to replace active drives every 3 years.
The old drives get put into service as backup drives. I spin down all the
drives but the OS when not in use for 30 min. Backups are placed on a
separate system, never the same system.

I have worked with many backup systems over the years, Tape, Raid, etc. I
never really found a solution that I liked, so I created my own.

For backups I use rsync over ssh and copy only changed files to another
system. Backups are very fast.

My current script can either pull or push a backup to or from a system. It
keeps ancopy of all files in a file structure the same as the master. It
has the ability to exclude folders or file types. I also move any changed
for deleted files to a separate folder with the date of the backup. So I
basically have versioning.

The only downside of this method is that I could not take my backup drive
and drop it in the server and boot it if I lost both boot drives. Loosing
both drives has only happened once due to a power supply failure.


With the cost of SSD drive being under $100.00 to me it is not worth the
trouble I would just get a 2nd SSD and Mirror it and do backups to another
drive.

I work in IT for a living, I have seen lots of failures, usually data lost
is on a raid 5 that looses a 2nd drive during the rebuild. I have seen it
many times. Do not count on raid as your only way to recover a system

Just a not also on a raided root FS. You can always add a 3rd raid to your
raid 1 then you can loose 2 drives and keep going. I used to take a 3rd
drive add it to the array, remove it, and take it off site for my backups
once a year. Just a thought, lots of ways to skin this cat, but it they
become time consuming or get in the way they will not be done on a regular
schedule.

Remember to cover both cheeks!

digid




On Thu, Jan 14, 2016 at 9:48 AM, Craig Huff <huffcslists at gmail.com> wrote:

> I have migrated my system disk to an SSD with /var mounted on a separate
> hard drive to limit wear on the SSD. For protection against the day the SSD
> fails, I'm thinking of mirroring it to a partition on an available hard
> drive.  It appears I can do this with either the traditional software raid
> approach using mdadm that looks a lot like what I did with Sun Solaris
> systems many years ago, or with dmraid, taking advantage of the Intel
> hardware (firmware?) support on my motherboard, although that may be an
> issue with the SSD on a SATA 3.0 port and the hard drive on a SATA 2.0
> port.  If I go ahead, I'll have to investigate that.
>
> As complicated as setting up and maintaining this system has been, I'm of
> mixed opinions on whether this would just be another step in the process or
> the straw that breaks the camel's back.
>
> I'd appreciate any advice or opinions.
>
> --
> Craig.
>
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