Re: RAID5 on different sized disks on low-end machine

Thanks for that information, that sounds like a good idea. The only
thing that concerns me is that in googling for LVM, I'm worried that
it's an extra layer of complication that may not be that stable as yet
since it needs devfs .. or am I talking out of my a$$ and have seen
too many scare stories? I like your idea of splitting the swap and
root partitions out to separate RAID1s.. I guess I could do something
similar even without LVM.

Thanks :)

Derek

/paranoid he's gonna choose the wrong thing and hose himself 6months
down the line.

On Wed, 12 Jan 2005 00:26:33 +0000, Robin Bowes
[off-list ref] wrote:

Derek Piper wrote:

quoted

Hi,

I revised my idea and thought about RAID 1+0 for some partitions,
since there are 4 drives. This outline below might clarify what I was
trying to mention earlier. Is this a feasible set-up that would be
bootable (kernel compiled-in md, I'm no stranger to compiling
kernels)? I'm interested to hear comments/opinions since I've never
done this before. Like I said, it'll be running on a Dual-pentium pro
200 (W6-LI) machine, I have no idea if machines of that vintage have
the 'cojones' for software raid or not.

My ideas of RAID1+0 / RAID5 disk system partitions
              MB
/dev/hde      60GB    57241   (from controller)
/dev/hdf      60GB    57241   (from controller)
/dev/hdg      60GB    57241   (from controller)
/dev/hdh      80GB    78125   (unconfirmed)

/dev/hd* = applies to all drives considered here

Device        MB      Type    GB      Mountpoint      MD device       RAIDed size (MB)        GB
/dev/hd*1     20      RAID1 + 0       0.02    /boot   /dev/md1        40      0.04
/dev/hd*2     192     RAID1 + 0       0.19    Swap    /dev/md2        384     0.38
/dev/hd*5     2048    RAID1 + 0       2       /       /dev/md5        4096    4
/dev/hd*6     2048    RAID5   2       /home   /dev/md6        6144    6
/dev/hd*7     52933   RAID5   51.69   /data   /dev/md7        158799  155.08

Does swap being raided make sense? I hear that sometimes it's a good
idea since a disk failure won't make you crash and then I heard
elsewhere that it doesn't matter and the kernel automatically raids
swap partitions anyway. I prepared the above in a spreadsheet btw so I
could work out partition sizes.

Thanks in advance again for any comments.

Derek

On Tue, 11 Jan 2005 13:47:20 -0500, Derek Piper [off-list ref] wrote:

quoted

Hi,

I am new to RAID / md devices, although I've used Linux for a number
of years. I decided it was high-time I had a RAID at home for
important things (email, web-sites, son's baby pics, mp3s etc.). I
happen to have a 3 Seagate 60GB hds and 1 80GB Seagate hd that I am
considering using for a RAID.

My question is this, is it possible (and even a good idea) to use all
4 hard drives as members of a 4 x 60GB RAID5 array by leaving 20GB of
the 80GB drive as a non-raided partition? I'll be using a Promise
Ultra TX2/100 controller.

i.e.

hde -> 60
hdf -> 60
hdg -> 60
hdh -> 60/20

I heard about RAID6 too, though I'm assuming that will use up another
disk's worth of disk space too.

i.e. RAID5 = 180GB usable size,wherease RAID6 = 120GB .. am I correct
in my thinking?

I know many of you use far larger hard drives, I'm just trying to use
the components I already had spare from a number of machines and
reorganize to a RAID-backed fileserver.

The machine is a dual pentium-pro 200 (320MB RAM) .. would that be a
dumb idea to use RAID5 on it because of the parity calculations
needed?

Further to that, would it be a smarter idea to use RAID1 on all 4 of
some small partition(s) at the start of the disks to house
boot/root/usr partitions, and only RAID5 on a larger 'data' area of
the drive that is more likely to be read than written to?

Derek,

I have a machine with 6 x 250GB SATA disks, but the configuration I use
would work just as well for you. Here's what I'd do:

Partition all your drives the same.
Create one small partition of 1GB, plus one large partition using up the
rest of the disk (i.e. around 59GB), *except* the 80GB drive. On this,
create a 1GB partition, a 59GB partition, plus a third partition using
up the rest of the disk (i.e. around 20GB)

Assuming these drives are /dev/hd[efgh], configure them as follows:

/dev/hd[ef]1    /dev/md0        /
/dev/hd[gh]1    /dev/md1        swap
/dev/hd[efgh]2  /dev/md2        lvm volume group
/dev/hdh3       -               use for whatever you want!

Now, use lvm to create logical volumes in your large volume group. I
have created /var, /use, and use the rest for /home.

These are my arrays:

[root@dude slimserver]# mdadm --detail --scan
ARRAY /dev/md1 level=raid1 num-devices=2
UUID=be8ad31a:f13b6f4b:c39732fc:c84f32a8
    devices=/dev/sdb1,/dev/sde1
ARRAY /dev/md2 level=raid1 num-devices=2
UUID=826170e2:cdd598d4:d212c9b1:6602deef
    devices=/dev/sdc1,/dev/sdf1
ARRAY /dev/md5 level=raid5 num-devices=5 spares=1
UUID=a4bbcd09:5e178c5b:3bf8bd45:8c31d2a1
    devices=/dev/sda2,/dev/sdb2,/dev/sdc2,/dev/sdd2,/dev/sde2,/dev/sdf2
ARRAY /dev/md0 level=raid1 num-devices=2
UUID=4b28338c:bf08d0bc:bb2899fc:e7f35eae
    devices=/dev/sda1,/dev/sdd1

These are the lvm logical volumes:

[root@dude slimserver]# lvdisplay
   --- Logical volume ---
   LV Name                /dev/audio_vg/usr_lv
   VG Name                audio_vg
   LV UUID                qseH0A-wKgo-xhB5-2tJ4-Qnxx-VOML-0eb43m
   LV Write Access        read/write
   LV Status              available
   # open                 1
   LV Size                10.00 GB
   Current LE             160
   Segments               1
   Allocation             inherit
   Read ahead sectors     0
   Block device           253:0

   --- Logical volume ---
   LV Name                /dev/audio_vg/var_lv
   VG Name                audio_vg
   LV UUID                nzH8uf-LhyU-o5My-tK48-ckaw-xzfL-esbfj4
   LV Write Access        read/write
   LV Status              available
   # open                 1
   LV Size                5.00 GB
   Current LE             80
   Segments               1
   Allocation             inherit
   Read ahead sectors     0
   Block device           253:1

   --- Logical volume ---
   LV Name                /dev/audio_vg/home_lv
   VG Name                audio_vg
   LV UUID                zbixtc-S6mb-MTVR-WXGw-dkjG-EU9q-WeZItv
   LV Write Access        read/write
   LV Status              available
   # open                 1
   LV Size                914.38 GB
   Current LE             14630
   Segments               1
   Allocation             inherit
   Read ahead sectors     0
   Block device           253:2

This is what my filesystems look like:

[root@dude slimserver]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/md0              1.4G  357M  985M  27% /
/dev/mapper/audio_vg-var_lv
                       5.0G  1.4G  3.3G  30% /var
/dev/mapper/audio_vg-usr_lv
                       9.9G  2.4G  7.0G  26% /usr
/dev/mapper/audio_vg-home_lv
                       915G  142G  764G  16% /home

And finally swap:

[root@dude slimserver]# swapon -s
Filename                                Type            Size    Used
Priority
/dev/md1                                partition       1469816 224     -1

R.
--
http://robinbowes.com

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-- 
Derek Piper - derek.piper@gmail.com
http://doofer.org/