Software projects/OS/Slackware/Advanced usage/RAID: Difference between revisions

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= WIP WIP WIP HURRAID =
= WIP WIP WIP HURRAID =
* Need to properly rebuild one array while completing.
* Need to properly rebuild one array while completing.
* For now, don't try this incomplete tutorial unless you have some RAID knowledge
* Once finished and this warning removed, go for it.


= RAID =
= RAID =
Line 6: Line 8:
* We will use the robust native Linux software RAID.
* We will use the robust native Linux software RAID.
* It's a feature that can be used on the Pandora, so let's have fun with it
* It's a feature that can be used on the Pandora, so let's have fun with it
* I will cover here only a RAID 1 (mirror) on two SD cards, as it should be the more interesting for a server usage because under read load, you can reach about 27MB/s against 16MB/s on one card.
* I will cover here only a RAID 1 (mirror) on two SD cards, as it should be the more interesting for a server usage because under read load, you should reach about 27MB/s against 16MB/s on one card.
* A SD + USB drive can also work although untested. As a two SD + USB drive.
* A SD + USB drive can also work although untested. Same with a two SD + USB drive configuration.
* This array will be mounted as /srv , the standard server folder.
* This array will be mounted as /srv , the standard server folder.


= Partitioning =
= Partitioning =
* So you have to partition your system SD card differently than the default SL4P setup.
* So you have to partition your system SD card a bit differently than the default SL4P setup.
* In this example, we will use the recommended minimal 8G card for the slot 1.
* In this example, we will use the recommended minimal 8G card for the slot 1.
* You can use a different sized card for the right slot. The minimum size is 4G for this second card, and we will use 4G in this example.
* You can use a different sized card for the right slot. To keep thing interesting, the minimum size is 4G for this second card, and we will use 4G in this example.
* The RAID 1 partitions must have the same exact size.
* The RAID 1 partitions must have the same exact size.


= Card 1 =
= Card 1 =
* Partition that way:
* Partition that way:
  6G ext2 for the system
  6G ext2 for the system.
  256M for the swap
  256M for the swap.
That's all for now, the third partition will be created under Slackware, and will be:
That's all for now, the third partition will be created under Slackware, and will be:
  1.5G RAID
  1.5G RAID.
* We will left 256M free. NEVER fill an entire drive with a RAID array. Drives, ie. all 8G, doesn't necessary offer the same exact capacity, so you can get in trouble if you add a drive 32MB short.
* We will left 256M free. NEVER fill an entire drive with a RAID array. Drives, ie. all 8G, doesn't necessary offer the same exact capacity, so you can get in trouble if you add a drive 32MB short.


= Card 2 =
= Card 2 =
  256M for the swap
  256M for the swap. Having swap on two different cards is a good thing.
That's all for now, the other partitions will be created under Slackware, and will be:
That's all for now, the other partitions will be created under Slackware, and will be:
  1.5G unformated RAID
  1.5G unformated RAID.
  2G unused. Do what you want with it.
  2G unused. Do what you want with it.


Line 48: Line 50:


= Create the RAID 1 array =
= Create the RAID 1 array =
* Load module ?
* The RAID devices names are md0, md1, md2 etc..
  mdadm --create /dev/md0 --level 1 --raid-devices 2 /dev/mmcblk0p3 /dev/mmcblk1p2
  mdadm --create /dev/md0 --level 1 --raid-devices 2 /dev/mmcblk0p3 /dev/mmcblk1p2


= Format the RAID array =
= Format the RAID array =
* As usual, we choose the Linux extended 2 filesystem.
  mkfs.ext2 /dev/md0
  mkfs.ext2 /dev/md0


Line 71: Line 76:
= Remove a drive from the array =
= Remove a drive from the array =
* It's likely to be the one in the right SD slot.
* It's likely to be the one in the right SD slot.
* Unmount the swap:
swapoff /dev/mmcblk1p1


= Repair the array =
= Repair the array =
* Depending the size of your RAID partition and he data on it, it can take a while.
* Depending the size of your RAID partition and he data on it, it can take a while.
* Mount the swap:
swapon /dev/mmcblk1p1

Revision as of 23:25, 17 April 2012

WIP WIP WIP HURRAID

  • Need to properly rebuild one array while completing.
  • For now, don't try this incomplete tutorial unless you have some RAID knowledge
  • Once finished and this warning removed, go for it.

RAID

  • http://en.wikipedia.org/wiki/RAID
  • We will use the robust native Linux software RAID.
  • It's a feature that can be used on the Pandora, so let's have fun with it
  • I will cover here only a RAID 1 (mirror) on two SD cards, as it should be the more interesting for a server usage because under read load, you should reach about 27MB/s against 16MB/s on one card.
  • A SD + USB drive can also work although untested. Same with a two SD + USB drive configuration.
  • This array will be mounted as /srv , the standard server folder.

Partitioning

  • So you have to partition your system SD card a bit differently than the default SL4P setup.
  • In this example, we will use the recommended minimal 8G card for the slot 1.
  • You can use a different sized card for the right slot. To keep thing interesting, the minimum size is 4G for this second card, and we will use 4G in this example.
  • The RAID 1 partitions must have the same exact size.

Card 1

  • Partition that way:
6G ext2 for the system.
256M for the swap.

That's all for now, the third partition will be created under Slackware, and will be: 

1.5G RAID.
  • We will left 256M free. NEVER fill an entire drive with a RAID array. Drives, ie. all 8G, doesn't necessary offer the same exact capacity, so you can get in trouble if you add a drive 32MB short.

Card 2

256M for the swap. Having swap on two different cards is a good thing.

That's all for now, the other partitions will be created under Slackware, and will be: 

1.5G unformated RAID.
2G unused. Do what you want with it.

Install SL4P

  • Uncompress the rootfs on the first SD card, first partition, put the card in your OP, and boot it.
  • Log in.

Backup /srv

  • As root:
mkdir /srv-save
mv /srv/* /srv-save/

Finalizing card 1 setup

  • As root:
cfdisk

Finalizing card 2 setup

  • As root:
cfdisk

Create the RAID 1 array

  • Load module ?
  • The RAID devices names are md0, md1, md2 etc..
mdadm --create /dev/md0 --level 1 --raid-devices 2 /dev/mmcblk0p3 /dev/mmcblk1p2

Format the RAID array

  • As usual, we choose the Linux extended 2 filesystem.
mkfs.ext2 /dev/md0

Make the RAID configuration permanent

mdadm --scan > /etc/mdadm.conf

Edit /etc/fstab and add these lines: 

/dev/mmcblk1p1   swap   swap   defaults           0  0
/dev/md0         /srv   auto   defaults,noatime   1  1

Final step

  • As root:
mount/dev/md0
mv /srv-save/* /srv/
rm -rf /srv-save/
  • That's it, you have now a RAID 1 array on your Pandora :^).

Some Practice

  • If you want to know how to repair a RAID array, let's simulate a failure.

Remove a drive from the array

  • It's likely to be the one in the right SD slot.
  • Unmount the swap:
swapoff /dev/mmcblk1p1

Repair the array

  • Depending the size of your RAID partition and he data on it, it can take a while.
  • Mount the swap:
swapon /dev/mmcblk1p1
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