Re: Software RAID

[Tom Spec]

>  You really do not want to do it this way. Setting up raid on a
>  partitions just seems like such a bad idea on so many levels. You
>  should do it on the entire disk. Last time I remember messing with it,
>  the setup screen for that was not capable of doing that. 
How do you propose to do "entire disk"?  Will you be using LVM on the system?

I have had very good success with the method I described, including several incidents of 
failed drives.  Clearly it's not as good as hardware RAID, but still I think
it is MUCH  better than nothing.  It is certainly the best mirroring solution
I have come across short of a hardware RAID controller.

Tom

Software RAID

[Zane C.Bowers]

On Fri, 23 Jun 2006 11:41:30 -0700 (PDT)
Tom Spec <samag70-ignore(a)yahoo.ca&gt; wrote:

>  > You really do not want to do it this way. Setting up raid on a
>  > partitions just seems like such a bad idea on so many levels. You
>  > should do it on the entire disk. Last time I remember messing with
>  > it, the setup screen for that was not capable of doing that.
>  
>  How do you propose to do "entire disk"?  Will you be using LVM on the
>  system?
>  
>  I have had very good success with the method I described, including
>  several incidents of failed drives.  Clearly it's not as good as
>  hardware RAID, but still I think it is MUCH  better than nothing.  It
>  is certainly the best mirroring solution I have come across short of
>  a hardware RAID controller. 
As far as I know it can't be done from installer. You create a mirror
using two entire disks and then slice it up. This requires installing,
setting up the raid, slicing the raid, rebooting, making it bootable
and migrating the installed stuff to it, and finally rebooting and
telling it to boot from one of the raided disks.

I've not had time to fully test this, but I am currently playing around
with it. I don't like the idea of mirroring partitions because
replacing a disk means having to repartition/slice the disk.

Software RAID

[Bruno Wolff III]

On Fri, Jun 23, 2006 at 14:21:38 -0500,
  "Zane C.B." <zanecb(a)midwest-connections.com&gt; wrote:
>  
>  I've not had time to fully test this, but I am currently playing around
>  with it. I don't like the idea of mirroring partitions because
>  replacing a disk means having to repartition/slice the disk. 
It should only take a couple of minutes to create appropiately sized
partitions on the replacement disk. If you expect to do this a lot, you
could even have a script set up ahead of time so that the time isn't spent
during an emergency.
By mirroring by partition, you have the option to replace a disk with a
different size disk.

Software RAID

[Nigel Wade]

Zane C.B. wrote:

> I don't like the idea of mirroring partitions because
>  replacing a disk means having to repartition/slice the disk.
>   
To copy the partition table from hda to hdc all you need is:

sfdisk -d /dev/hda | sfdisk -f /dev/hdc

How do you replace an entire disk in a running raid?


To the OP:

The RedHat docs have a basic guide on setting up a RAID 1 mirror during 
installation:
http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/sysadmin-guid...


-- 
Nigel Wade, System Administrator, Space Plasma Physics Group,
             University of Leicester, Leicester, LE1 7RH, UK
E-mail :    nmw(a)ion.le.ac.uk
Phone :     [phone], Fax : [phone]

Software RAID

[Mogens Kjaer]

Tom Spec wrote:
...
>  Clearly it's not as good as hardware RAID, but still I think
>  it is MUCH  better than nothing. 
The SCSI hardware RAID controllers I've seen in the past
(HP/Compaq SmartArray and an IBM serveraid) have all
had worse performance than using Linux software RAID.

Software RAID (RAID 5 in my case) was 2x faster writing and
3x faster reading than hardware RAID.

Mogens

-- 
Mogens Kjaer, Carlsberg A/S, Computer Department
Gamle Carlsberg Vej 10, DK-2500 Valby, Denmark
Phone: [phone], Fax: [phone]
Email: mk(a)crc.dk Homepage: http://www.crc.dk

Software RAID

[Bruno Wolff III]

On Fri, Jun 23, 2006 at 11:41:30 -0700,
  Tom Spec <samag70-ignore(a)yahoo.ca&gt; wrote:
>  
>  I have had very good success with the method I described, including several incidents of
>
>  failed drives.  Clearly it's not as good as hardware RAID, but still I think
>  it is MUCH  better than nothing.  It is certainly the best mirroring solution
>  I have come across short of a hardware RAID controller. 
Actually it isn't that clear. Software raid can give you better performance
than hardware raid. You also don't get locked into specific hardware.
Unless you are buying raid cards with battery backed cache or cannot spare
the cpu overhead, you are probably going to be better off with software
raid.