[mythtv-users] RAID5 ATA IDE hardware card recommendations formythbackend machine

Yan-Fa Li yanfali at best.com
Wed Dec 8 20:47:36 UTC 2004

Being cheap, I still think that I would rather not use the onboard RAID 
implementation, even of a well respected card like 3ware, because of the 
lack of low-level access to the actual drive which impacts recovery and 

In my experience, most problems with RAID tend to be:

	a. sectors going bad - transient
	b. drives going bad  - fatal

Sectors going bad, pretty much always requires taking the drive out of 
service and running the vendor provided sector reallocation tool.  I'm 
hoping one day you'll be able to initiate this from SMART commands 
directly but as of now this is not the case.

Drives going bad is self explanatory.

In my experience, once a drive has been added to a Hardware RAID set, 
you can't access it directly.  This makes using the Hard Drive vendor 
recovery tools impossible, since the drive is hidden from low-level 
access.  This requires you to either remove it from the set to perform 
repair tasks or take it out of the system and put it into a standalone 
box where the repair can be performed.

At least with Soft RAID solutions, you have the additional flexibility 
of being able to run the HD vendor tool directly on the drive. 
Additionally Soft RAID can use physical disk partitioning on the drive 
to speed up recovery and guarentee performance.

Here's something I've been playing with recently after getting the idea 
off of other Soft RAID users.  I set up a two 160GB drives.  Then I 
partitioned each of them into 4 x 40GB partitions.  I made each pair of 
partitions into RAID1 sets.  I then LVM'd all the RAID1 sets into a 
single partition and formatted them using XFS.

So, as you may ask, why the crazy partitioning scheme ?  Speeding up 
resync time.  The biggest problem with large RAID sets is that it takes 
a longer and longer to resync.  Because the majority of problems with 
RAID arrays are related to sector failure, large RAID1 sets are 
suceptible to being knocked out with only a few bad sectors.  This means 
excessive resync time and unnecessary wear and tear on the drive.

Bottom line: I'd rather resync a 40GB partition than a 160GB one.

As a side benefit there now are some interesting things you can do 
related to performance.  This is an old trick streaming video guys used 
to use when disks had much lower performance.  Disk performance is 
related to how far you are from the spindle.

Think of each of the RAID sets as a zone, with Zone 1, being closest to 
the spindle and having a higher areal density  and Zone 4 the outer most 
part of the disk being the slowest.  If one wanted, one could use the 
different zones of the disk for different jobs.  For example, it would 
make sense to put TV buffering on the fastest part of the drive, so you 
could use Zone 1 for TV buffering.  Zone 4 however is all about storage 
and one could use it for long term file or video storage, or even not at 
all if performance were critical.


Jurgen Kramer wrote:
> On Tue, 2004-12-07 at 16:51 -0500, Andrew Plumb wrote:
>>Hi Everyone,
>>For those who do use hardware RAID5 cards for ATA IDE drives, which
>>cards have you (not) had success with, for use in a mythtvbackend
>>machine?  Or in any Linux-based machine for that matter?
>>I'm pondering picking up something like a Promise FastTrak SX4000.
> I can recommend the 3ware 9000 series (SATA), it is a bit expansive but
> is otherwise rock solid and has good Linux support.
> Jurgen
>>mythtv-users mailing list
>>mythtv-users at mythtv.org
>>mythtv-users mailing list
>>mythtv-users at mythtv.org

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