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Old 07-31-2008, 07:40 PM
Uwe Geercken
 
Default Software Raid

hello everybody,

the schoolyear is over here in germany and I have taken the server
home for maintenance. I built this server at the beginning of the year
and been teaching linux at our local school to students of 6 to 8th
class.

at the time I setup the system, I have used one harddisk for the
system and one for the home directories of the students. so these are
on seperate drives.

I am now thinking putting in a second drive and use software raid so
that I will have faster reads. my first thought was to use raid for
the system and still have the home folders on a seperate drive. or
maybe I should put home and the system on the same drive and use raid
for both?

could somebody please give me an advice?

rgds,

uwe


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Old 08-01-2008, 09:47 AM
Gavin McCullagh
 
Default Software Raid

Hi,

On Thu, 31 Jul 2008, Uwe Geercken wrote:

> at the time I setup the system, I have used one harddisk for the
> system and one for the home directories of the students. so these are
> on seperate drives.

What sizes are the respective drives? Are they IDE, SATA, SCSI?

> I am now thinking putting in a second drive and use software raid so
> that I will have faster reads. my first thought was to use raid for
> the system and still have the home folders on a seperate drive. or
> maybe I should put home and the system on the same drive and use raid
> for both?

I presume you're talking about MD (linux kernel software raid). Presumably
it can read off the disks independently so you should probably get improved
read speeds. To my mind though, reliability is the best feature of RAID1.

http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1_performance

If you can get both the system and the home directories onto RAID1, you're
system will keep running in the event of a single disk failure. Disk
failure is remarkably common these days.

Migrating the running system to software RAID is not easy, so you may find
it easiest to reinstall which is a bit of a downside. Presumably you can
just back up and restore the home directories with tar. For the system, if
you have sufficient space and don't wish to reinstall, you could possibly
do something like

1. Shrink your / partition by 50% using gnu parted
2. Create a new equal sized partition in the resulting space. Make it of
type linux-raid
3. Create a larger raid partition on the new disk.
4. Use mdadm to create a raid1 array using the two raid partitions.
5. Format the raid partition ext3 (or whatever you're using)
6. Reboot and make sure the raid partition comes back up.
7. Drop to single user mode and use something like cpio or rsync to sync
the new raid partition with the old one.
8. Configure grub with extra boot items to boot onto the new partition
9. Reboot using the new grub entry and say a prayer (if it doesn't work,
you should be able to boot onto the old partition anyway).
10.Once you're up on the new partition, you can re-run grub-install,
delete the old non-raid partition, expand the existing one back into the
freed space, expand the raid array into the space and finally expand the
root filesystem on the bigger partition.

These instructions are untested and I've probably missed something.
Frankly, I'd highly recommend the reinstall, backing up your config first
of course!

Gavin


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Old 08-01-2008, 08:52 PM
Uwe Geercken
 
Default Software Raid

hi gavin,

thanks for your feedback which is great as always !!!

I have currently two sata disks as indicated one with the system
(250GB Samsung) and one with home (500GB Samsung).

on the home drive there is about 2GB of data, so I can put that on a dvd.

the system drive has edubuntu 7.10 and I will upgrade to 8.04 anyway
by reinstalling from scratch. we haven't really installed a lot of
programs. basically just java, mysql some codecs and some games. I can
install all this quite quickly from the repository.

thanks for your words on the installation of raid. they will be very
useful. as I am doing the LPI right now (6 of 9 month done) I have
already setup raid during the course and I also have some
documentation, which will get me going.

is there anything that I should not put on the raid or is not worth
it, like eg. swap?

I will probably put system and home on one drive and have another disk
for the raid because 500 GB are really enough for our purposes. and I
can use the thrid disk for downloads or setting up a mirror of a
repository (which I did in the past).

I think about it over the weekend.

thanks again,

uwe



Zitat von Gavin McCullagh <gmccullagh@gmail.com>:

> Hi,
>
> On Thu, 31 Jul 2008, Uwe Geercken wrote:
>
>> at the time I setup the system, I have used one harddisk for the
>> system and one for the home directories of the students. so these are
>> on seperate drives.
>
> What sizes are the respective drives? Are they IDE, SATA, SCSI?
>
>> I am now thinking putting in a second drive and use software raid so
>> that I will have faster reads. my first thought was to use raid for
>> the system and still have the home folders on a seperate drive. or
>> maybe I should put home and the system on the same drive and use raid
>> for both?
>
> I presume you're talking about MD (linux kernel software raid). Presumably
> it can read off the disks independently so you should probably get improved
> read speeds. To my mind though, reliability is the best feature of RAID1.
>
> http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1_performance
>
> If you can get both the system and the home directories onto RAID1, you're
> system will keep running in the event of a single disk failure. Disk
> failure is remarkably common these days.
>
> Migrating the running system to software RAID is not easy, so you may find
> it easiest to reinstall which is a bit of a downside. Presumably you can
> just back up and restore the home directories with tar. For the system, if
> you have sufficient space and don't wish to reinstall, you could possibly
> do something like
>
> 1. Shrink your / partition by 50% using gnu parted
> 2. Create a new equal sized partition in the resulting space. Make it of
> type linux-raid
> 3. Create a larger raid partition on the new disk.
> 4. Use mdadm to create a raid1 array using the two raid partitions.
> 5. Format the raid partition ext3 (or whatever you're using)
> 6. Reboot and make sure the raid partition comes back up.
> 7. Drop to single user mode and use something like cpio or rsync to sync
> the new raid partition with the old one.
> 8. Configure grub with extra boot items to boot onto the new partition
> 9. Reboot using the new grub entry and say a prayer (if it doesn't work,
> you should be able to boot onto the old partition anyway).
> 10.Once you're up on the new partition, you can re-run grub-install,
> delete the old non-raid partition, expand the existing one back into the
> freed space, expand the raid array into the space and finally expand the
> root filesystem on the bigger partition.
>
> These instructions are untested and I've probably missed something.
> Frankly, I'd highly recommend the reinstall, backing up your config first
> of course!
>
> Gavin
>
>
> --
> edubuntu-users mailing list
> edubuntu-users@lists.ubuntu.com
> Modify settings or unsubscribe at:
> https://lists.ubuntu.com/mailman/listinfo/edubuntu-users
>



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