On 03/08/2012 13:18, Stan Hoeppner wrote:
On 8/3/2012 12:27 AM, Flynn wrote:
My RAID6 is actually a little bit odd in that the drives are split into
10 partitions. All the partition 5's are a RAID6; all the partition 6's
are a RAID6; etc.
md offered the ability, so you _could_ create such a monstrosity. But
you never bothered to consider if you _should_
The primary function of RAID is to protect your data in the event of a
_disk_ failure. Creating multiple arrays from _partitions_ on the same
set of physical disks does nothing to protect one from disk failure.
That's not how I understand the disk layout - if I'm right, it is still
a monstrosity, but one that will offer protection on disk failure.
As I read it, he has this (prior to adding the new disk):
md0 = raid6(sda5, sdb5, sdc5, sdd5, sde5)
md1 = raid6(sda6, sdb6, sdc6, sdd6, sde6)
...
md9 = raid6(sda14, sdb14, sdc14, sdd14, sde14)
If that's the case, then it will be an administrative mess (as the OP is
now experiencing), but it will protect the data, and if the LVM is a
linear concatenation of these then performance normally will be okay.
Of course, if the LVM tries to use a stripe of these arrays, it will be
terrible - and rebuild/reshape will involve massively inefficient head
movement (as you noted).
What it can do is cause massive problems for the elevator when you try
to reshape 10 arrays simultaneously, which just happen to reside on the
same set of disks. By doing this you force the heads on the drives into
a massive random seek pattern, bumping all over the platters, top to
bottom. This is likely what caused, or is directly related to, your crash.
Suggestions very welcome.
Backup what you need to external storage. Blow the entire mess away.
Start over from scratch, and build a single RAID6 array, as you should
have in the first place.
If the OP can manage it, then I agree.
md allows the use of partitions, but not so you can create 50 arrays on
the same set of disks, shooting yourself in the foot. Similarly, most
cars can travel at velocities over 120 mph, but most people have enough
sense not to attempt driving that fast.
I have sometimes used multiple arrays like this:
md0 = raid1,n4(sda1, sdb1, sdc1, sdd1) for /boot (makes grub happy)
md1 = raid5(sda2, sdb2, sdc2, sdd2) for everything else
But this particular setup seems very odd to me - I would love to know
the reasoning behind it.
Learn the difference between "Can I?" and "Should I?". You never
bothered to consider the latter when you built this. Please consider it
now, for your sake.
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