[CentOS] Re: Anaconda doesn't support raid10

[Scott Silva]

Ruslan Sivak spake the following on 5/7/2007 1:44 PM:
> Toby Bluhm wrote:
>> Ruslan Sivak wrote:
>>> Ross S. W. Walker wrote:
>>>>> -----Original Message-----
>>>>> From: centos-bounces at centos.org
>>>>> [mailto:centos-bounces at centos.org] On
>>>>> Behalf Of Ruslan Sivak
>>>>> Sent: Monday, May 07, 2007 12:53 PM
>>>>> To: CentOS mailing list
>>>>> Subject: [CentOS] Anaconda doesn't support raid10
>>>>>
>>>>> So after troubleshooting this for about a week, I was finally able
>>>>> to create a raid 10 device by installing the system, copying the md
>>>>> modules onto a floppy, and loading the raid10 module during the
>>>>> install.
>>>>> Now the problem is that I can't get it to show up in anaconda.  It
>>>>> detects the other arrays (raid0 and raid1) fine, but the raid10
>>>>> array won't show up.  Looking through the logs (Alt-F3), I see the
>>>>> following warning:
>>>>>
>>>>> WARNING: raid level RAID10 not supported, skipping md10.
>>>>> I'm starting to hate the installer more and more.  Why won't it let
>>>>> me install on this device, even though it's working perfectly from
>>>>> the shell?  Why am I the only one having this problem?  Is nobody
>>>>> out there using md based raid10?     
>>>>
>>>> Most people install the OS on a 2 disk raid1, then create a separate
>>>> raid10 for data storage.
>>>>
>>>> Anaconda was never designed to create RAID5/RAID10 during install.
>>>>
>>>> -Ross
>>>>
>>>>   
>>>
>>> Whether or not it was designed to create a Raid5/raid10, it allows
>>> the creating of raid5 and raid6 during install.  It doesn't, however,
>>> allow the use of raid10 even if it's created in the shell outside of
>>> anaconda (or if you have an old installation on a raid10).
>>> I've just installed the system as follows
>>>
>>> Raid1 for /boot with 2 spares (200mb)
>>> raid0 for swap  (1GB)
>>> raid6 for / (10GB)
>>>
>>> after installing, I was able to create a raid10 device and
>>> successfully mount and automount by using /etc/fstab
>>>
>>> Now to test what happens when a drive fails.  I pulled out the first
>>> drive - Box refuses to boot.  Going into rescue mode, I was able to
>>> mount /boot, was not able to mount the swap drive (as to be expected,
>>> as it's a raid0), was also not able to mount the / for some reason,
>>> which is a little surprising.
>>> I was able to mount the raid10 parition just fine.
>>> Maybe I messed up somewhere along the line.  I'll try again, but it's
>>> disheartening to see that a raid6 array would die after one drive
>>> failure, even if it was somehow my fault.
>>> Also assuming that the raid5 array could be recovered, what would I
>>> do with the swap partition?  Would I just recreate it from the space
>>> in the leftover drives and would that be all that I need to boot?
>>> Russ
>>>
>>>
>>
>> Russ,
>>
>> Nothing here to help you (again - :) just looking down the road a
>> little. If you do get this thing working the way you want, will you be
>> able to trust it to stay that way?
>>
> Well, it's been my experience, that in linux, unlike windows, it might
> take a while to get things the way you want, but once you do, you can
> pretty much trust it to stay that way.
> So yea, this is what I'm looking to do here.  I want to set up a system,
> that will live after 1 (or possibly 2) drive failures.  I want to know
> what I need to do ahead of time, so that I can be confident in my set
> up, and know what to do in case disaster strikes.
> 
> Russ
If you have the hardware, or the money, you can make a system pretty durable.
But you get to a point that the gains aren't worth the cost. You can get a
system to 3 "9's" fairly easy, but the cost to get to 4 "9's" is much more. If
you want something better than 4 "9's", you will have to look at clustering,
because a single reboot in a month can shoot down your numbers.

If you want total reliability, you will need hot spares and a raid method that
builds quickly, and you will need regular backups.

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