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Re: LVM RAID5 with missing disk?

Gary Dale <extremegroundmailer@gmail.com> writes:

> On 04/12/14 12:51 PM, Dan Ritter wrote:
>> On Thu, Dec 04, 2014 at 02:13:59PM +0100, mad wrote:
>>> Hi!
>>> I wanted to create a RAID5 with lvm. The basic setup is something like
>>> lvcreate --type raid5 -i 2 -L 1G -n my_lv my_vg
>>> which would mean 3 physical drives would be used in this RAID5. But can
>>> I specify that one drive is missing as it is possible with mdadm?
>> I don't think so, no. You can create your RAID with mdadm and
>> put LVM on top of that.
>> In general I strongly recommend against using RAID5. RAID1, 10,
>> or 6 are all better options if your data's availability is
>> important to you.
>> -dsr-
> Sorry, but there are good reasons to use RAID 5 and better reasons to
> NOT use RAID 10. RAID 1 and RAID 5 are both immune to single disk
> failures in their most common configurations (1 or more data disks
> with 1 parity disk).

The problem is not that RAID5 does not provide resilience against a
single disk failure. The problem is that with modern disk capacities,
the chances of *another* disk failing while the array is rebuilding have
significantly risen.

Especially when all the disks came out of the the same batch, they tend
to fail at similar times. I know Best Practice is to mix disks in RAID
arrays, but who actually practices that, instead of just taking the risk
of failure and covering it with a higher RAID level, like RAID6 in this

"We will need a longer wall when the revolution comes."
    --- AJS, quoting an uncertain source.

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