[mythtv-users] An LVM'd drive died! What do I do...

Brandon Beattie brandon+myth at linuxis.us
Thu Oct 27 14:31:42 EDT 2005


On Thu, Oct 27, 2005 at 05:04:14PM +0100, David wrote:
> >  Raid to several of us who run TB+ LVM's for a myth box
> >is a dumb idea.
> >
> No it's not.

I said several, not everyone. :)  My reasons for not doing raid are $100
for an extra HD drive that doesn't add raw space, matching partition 
sizes (Big annoyance), you're only as fast as the slowest disk when
doing massive data transfers (HD Video), I can't fit more than 6 drives
in my case, most hardware IDE raid cards can't do more than 15MB/s
unless you spend $300+, I've seen _many_ hardware IDE raid cards go bad,
and some have destroyed the entire raid subsystem.  Software raid is
good, but has annoyances too.  But the #1 reason I don't use raid is 
it's not a safe bet anyhow.  In my experience the main benifit of raid
is availiblity, not protecting data.  Since I have to admit that
something _could_ go wrong, even when using raid, and could I lose it 
(Since backing up over a TB of storage is very painful and costly) I
conclude it's not worth the time or money dealing with raid.  If we were
talking about SCSI, heavily tested rack systems designed for reliability
that's one thing, but we're talking about home built PC's and they
simply do not offer the reliability.  I see more data loss from other
things than I do from a hard drive going bad.  This has been my
experience, and people are welcome to disagree.

Some various, non HD failures are as follows, on a chance of 1 to 10 of 
a problem happening, where 10 is where an average quality drive failure
is.

Power supply frying drives:
 2 Too many drives on the PSU  
 3 PSU quality is subpar
 1 PSU just goes nuts
Overheating
 1 Someone going for a quiet system and the drives run too hot
 1 PSU can't get cool air and fries itself
Raid
 1 IDE Hardware Raid card has a bug
 2 IDE Hardware Raid card goes bad and corrupts data
 2 IDE Hardware Raid card goes bad, replacement expensive if even
    availible 3 year later.
 2 Software raid primary partition gets corrupted
 4 User Error when working with Raid and being new
 1 User Error when working with Raid and making a dumb mistake
Other
 4 Filesystem corruption 
 2 Software bug
 1 HD goes out and fries other HD's connected to the same power cable
 1 Motherboard goes out and fries the PCI cards in it
 2 User thinks things are setup right and they're not
 3 User gets tired of current Raid system and wants to redesign from the
    beginning.
 1 Drive goes out and user can't afford to go buy a new one right then
 1 User needs to use the drive in another system
 .1 Home burns down, system stolen, wife beats it with an axe.
 ? I'm sure there are others I haven't listed.

The bottom line as I see it is cheap (That's about sums it up) Raid 
solution buys you mostly availability and only
a small portion of reliability in the grand scheme, not safety.
If you want safety you have to back things up to something not associate
with the first copy.  If someone wanted to buy a Dell PowerEdge 2500
with a PERC4 raid controller and 10K RPM Seagate SCSI drives, then
that's a pretty safe solutions, but we're not talking about this type of
system or raid hardware.  

For each person raid will be more or less important (Regardless if
they're thoughts are facts or fiction).  What every person needs to
decide is if the money, time, cost, and availability and realiability
provided is worth not missing Lost (Which everyone else you know has
recorded too).  

I did raid 1 for my root FS, raid 5 for some storage, and raid 0 for
shows in a TB mythbox for some time (Besides all the servers I've run
for companies in the past).  Raid had more downsides, pitfalls and
annoyances than benefits _for_a_MythBox_, and that was my conclusion.

Raid is also too limiting in it's functionality.  Once you set things up
you can't change much.  You can claim you'll never want to change
things, ever, but that's not going to be true for most people.  For
those with bottomless pockets, sure, go dump $5k into a fileserver with
10 500GB drives doing raid 10, but for the average user who reads
mythtv-users and has to save for a month or two to get a single 200GB
drive to add to his collection of 60GB, and 120GB drives, raid just is
not going to make their myth viewing better.

I only am speaking up because I see way too many people acting like they
know without a doubt that this thing called Raid that they've heard of 
and used for a year is the best thing for everyone and their dog,
and claiming Raid is what everyone should do, when it just isn't.  Those
people are going to cause a lot of people headaches, waste their money,
and cause other problems.

--Brandon


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