RAID 5 with different size disks

[Fajar Priyanto]

Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?
Thank you very much,

[Gordon Messmer]

Post by Fajar Priyanto
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

No, it isn't. RAID5, by design, requires units of the same size.

[Jerel Harwood]

Post by Gordon Messmer

Post by Fajar Priyanto
Is it possible to setup a RAID 5 array using different size disks? Such

as hda

Post by Gordon Messmer

Post by Fajar Priyanto
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

No, it isn't. RAID5, by design, requires units of the same size.

Depending on what you are using to create the RAID5 (software vs. hardware.)
It is possible to create a raid5 with the disk configuration you spec, but
due to the nature of raid5 you will be wasting massive amounts of disk space
as the max amount of disk space it will use per disk is directly relational
to the smallest sized disk you use. Thus it will only use 9GB of the 36,
9GB of the 40 and 9GB of the 80GB drives each.

You will only get 4 x 9GB = 36GB of disk space (disk 5 is used for Parity)

Instead you could mirror (RAID1) the 2 80GB drives and put your critical
data on them.

-J Harwood

[Fajar Priyanto]

Post by Jerel Harwood
Depending on what you are using to create the RAID5 (software vs.
hardware.) It is possible to create a raid5 with the disk configuration you
spec, but due to the nature of raid5 you will be wasting massive amounts of
disk space as the max amount of disk space it will use per disk is directly
relational to the smallest sized disk you use. Thus it will only use 9GB
of the 36, 9GB of the 40 and 9GB of the 80GB drives each.
You will only get 4 x 9GB = 36GB of disk space (disk 5 is used for Parity)
Instead you could mirror (RAID1) the 2 80GB drives and put your critical
data on them.

Ok.
If I setup the mirror using software raid, and then later my OS disk fails,
will the new installation of Linux be able to recognize the existing mirror,
thus the data in it?

Or should I just install all OS in the mirror?
Thanks you,

[John Summerfied]

Post by Fajar Priyanto
Ok.
If I setup the mirror using software raid, and then later my OS disk fails,
will the new installation of Linux be able to recognize the existing mirror,
thus the data in it?
Or should I just install all OS in the mirror?
Thanks you,

Back it up regularly to the raid array.

[John Summerfied]

Post by Fajar Priyanto
Ok.
If I setup the mirror using software raid, and then later my OS disk fails,
will the new installation of Linux be able to recognize the existing mirror,
thus the data in it?
Or should I just install all OS in the mirror?
Thanks you,

Back it up regularly to the raid array.

[jludwig]

Post by Fajar Priyanto

Post by Gordon Messmer

Post by Fajar Priyanto
Is it possible to setup a RAID 5 array using different size disks? Such

as hda

Post by Gordon Messmer

Post by Fajar Priyanto
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

No, it isn't. RAID5, by design, requires units of the same size.

Depending on what you are using to create the RAID5 (software vs.
hardware.) It is possible to create a raid5 with the disk configuration you
spec, but due to the nature of raid5 you will be wasting massive amounts of
disk space as the max amount of disk space it will use per disk is directly
relational to the smallest sized disk you use. Thus it will only use 9GB
of the 36, 9GB of the 40 and 9GB of the 80GB drives each.
You will only get 4 x 9GB = 36GB of disk space (disk 5 is used for Parity)
Instead you could mirror (RAID1) the 2 80GB drives and put your critical
data on them.
-J Harwood

As far as different size drives from MDADM(8) ;

DESCRIPTION
RAID devices are virtual devices created from two or more real block
devices. This allows multiple devices (typically disk drives or partitions
there-of) to be combined into a single device to hold (for example) a single
filesystem.

[Fajar Priyanto]

Post by Jerel Harwood
Depending on what you are using to create the RAID5 (software vs.
hardware.) It is possible to create a raid5 with the disk configuration you
spec, but due to the nature of raid5 you will be wasting massive amounts of
disk space as the max amount of disk space it will use per disk is directly
relational to the smallest sized disk you use. Thus it will only use 9GB
of the 36, 9GB of the 40 and 9GB of the 80GB drives each.
You will only get 4 x 9GB = 36GB of disk space (disk 5 is used for Parity)
Instead you could mirror (RAID1) the 2 80GB drives and put your critical
data on them.

Ok.
If I setup the mirror using software raid, and then later my OS disk fails,
will the new installation of Linux be able to recognize the existing mirror,
thus the data in it?

Or should I just install all OS in the mirror?
Thanks you,

[jludwig]

Post by Fajar Priyanto

Post by Gordon Messmer

Post by Fajar Priyanto
Is it possible to setup a RAID 5 array using different size disks? Such

as hda

Post by Gordon Messmer

Post by Fajar Priyanto
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

No, it isn't. RAID5, by design, requires units of the same size.

Depending on what you are using to create the RAID5 (software vs.
hardware.) It is possible to create a raid5 with the disk configuration you
spec, but due to the nature of raid5 you will be wasting massive amounts of
disk space as the max amount of disk space it will use per disk is directly
relational to the smallest sized disk you use. Thus it will only use 9GB
of the 36, 9GB of the 40 and 9GB of the 80GB drives each.
You will only get 4 x 9GB = 36GB of disk space (disk 5 is used for Parity)
Instead you could mirror (RAID1) the 2 80GB drives and put your critical
data on them.
-J Harwood

As far as different size drives from MDADM(8) ;

DESCRIPTION
RAID devices are virtual devices created from two or more real block
devices. This allows multiple devices (typically disk drives or partitions
there-of) to be combined into a single device to hold (for example) a single
filesystem.

[Joel Jaeggli]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

if you think about it raid-5 is just a special case of raid-0 your
capacity is going to be limited by the size of the smallest drive... in
this case you'll get a lot more capacity just but setting up a mirror on
the two 80GB drives.

joelja

Post by Fajar Priyanto
What are the impact and consequences?
Thank you very much,

[Jeff Vian]

Post by Joel Jaeggli

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

if you think about it raid-5 is just a special case of raid-0 your
capacity is going to be limited by the size of the smallest drive... in
this case you'll get a lot more capacity just but setting up a mirror on
the two 80GB drives.

Raid 5 and raid 0 are very different animals.

Raid 0 is striped. Any single physical device fails and everything is
gone. There is no redundancy and multiple failure points.

Raid 5, while it is striped, also has a redundant parity stripe. Any
single drive failing does not lose data since the lost stripe can be
rebuilt from the parity stripe. The data on any one drive is copied to
the parity stripe on all the other drives. A single drive failure can
be tolerated with no data loss. In order for data to be lost this would
require 2 simultaneous failures.

Very different in functionality and in redundancy/fault tolerance.

Post by Joel Jaeggli
joelja

Post by Fajar Priyanto
What are the impact and consequences?
Thank you very much,

--
--------------------------------------------------------------------------
Joel Jaeggli Unix Consulting joelja at darkwing.uoregon.edu
GPG Key Fingerprint: 5C6E 0104 BAF0 40B0 5BD3 C38B F000 35AB B67F 56B2

[Jeff Vian]

Post by Joel Jaeggli

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

if you think about it raid-5 is just a special case of raid-0 your
capacity is going to be limited by the size of the smallest drive... in
this case you'll get a lot more capacity just but setting up a mirror on
the two 80GB drives.

Raid 5 and raid 0 are very different animals.

Raid 0 is striped. Any single physical device fails and everything is
gone. There is no redundancy and multiple failure points.

Raid 5, while it is striped, also has a redundant parity stripe. Any
single drive failing does not lose data since the lost stripe can be
rebuilt from the parity stripe. The data on any one drive is copied to
the parity stripe on all the other drives. A single drive failure can
be tolerated with no data loss. In order for data to be lost this would
require 2 simultaneous failures.

Very different in functionality and in redundancy/fault tolerance.

Post by Joel Jaeggli
joelja

Post by Fajar Priyanto
What are the impact and consequences?
Thank you very much,

--
--------------------------------------------------------------------------
Joel Jaeggli Unix Consulting joelja at darkwing.uoregon.edu
GPG Key Fingerprint: 5C6E 0104 BAF0 40B0 5BD3 C38B F000 35AB B67F 56B2

[Matt Morgan]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?
Thank you very much,

If you are experimenting with software RAID, you can make a 9Gb
partition on each of the drives, and add them to a RAID 5 array. Then
use the remaining space on the drives however you see fit (like
mirroring the remainder of the 80GB drives, and perhaps the 36 and
some of the 40).

That would be unsustainably complicated for a production system, in my
opinion. Drives are pretty cheap--just buy two 250GB drives and mirror
them, or buy two more 80GB drives and get rid of the 9, 36, and 40.

[John Summerfied]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?
Thank you very much,

Apart from comments by others re sizing, trying to use both disks on an
ATA connector at the same time serious hurts performance. As root, try this:

hdparm -t /dev/hda&
hdparm -t /dev/hdb

The ampersand is important.

I imagine you can play games with lvm and create equal-sized virtual
volumes, but again, watch that performance fall off.


You can address the first performance problem by adding ATA disk
controllers on PCI cards.

[Jeff Vian]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?

With software raid 5, you can use different size disks.
The requirement is that you create virtual devices (raid partitions) for
use, and all those must be the same size.

For example, the 9gb +36gb +40gb drives could be used to create 9
virtual raid devices of 9gb each and you would have 8 x 9 -> 72gb of
raid array.
This is not necessarily the best way to go since 4 of those virtual raid
devices would be on a single physical device.

However, you could create multiple raid arrays as you suggest and would
still have more than 80gb of unused space with each array spread across
several physical disks..

device 1 9gb on each hda, hdb, hdc, hdd, hde -> 5 X 9gb -> 36gb of
usable space
device 2 27gb on each hdb, hdc, hdd, hde -> 4 x 27gb -> 81gb usable
space.

this would leave about 4gb on hdc and 44gb on each of hdd & hde
unallocated.

Post by Fajar Priyanto
Thank you very much,
--
Fajar Priyanto | Reg'd Linux User #327841 | Linux tutorial
http://linux2.arinet.org
09:36:07 up 1:42, 2.6.14-1.1653_FC4 GNU/Linux
Let's use OpenOffice. http://www.openoffice.org

[Fajar Priyanto]

Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?
Thank you very much,

[Gordon Messmer]

Post by Fajar Priyanto
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

No, it isn't. RAID5, by design, requires units of the same size.

[Jerel Harwood]

Post by Gordon Messmer

Post by Fajar Priyanto
Is it possible to setup a RAID 5 array using different size disks? Such

as hda

Post by Gordon Messmer

Post by Fajar Priyanto
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

No, it isn't. RAID5, by design, requires units of the same size.

Depending on what you are using to create the RAID5 (software vs. hardware.)
It is possible to create a raid5 with the disk configuration you spec, but
due to the nature of raid5 you will be wasting massive amounts of disk space
as the max amount of disk space it will use per disk is directly relational
to the smallest sized disk you use. Thus it will only use 9GB of the 36,
9GB of the 40 and 9GB of the 80GB drives each.

You will only get 4 x 9GB = 36GB of disk space (disk 5 is used for Parity)

Instead you could mirror (RAID1) the 2 80GB drives and put your critical
data on them.

-J Harwood

[Joel Jaeggli]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.

if you think about it raid-5 is just a special case of raid-0 your
capacity is going to be limited by the size of the smallest drive... in
this case you'll get a lot more capacity just but setting up a mirror on
the two 80GB drives.

joelja

Post by Fajar Priyanto
What are the impact and consequences?
Thank you very much,

[Matt Morgan]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?
Thank you very much,

If you are experimenting with software RAID, you can make a 9Gb
partition on each of the drives, and add them to a RAID 5 array. Then
use the remaining space on the drives however you see fit (like
mirroring the remainder of the 80GB drives, and perhaps the 36 and
some of the 40).

That would be unsustainably complicated for a production system, in my
opinion. Drives are pretty cheap--just buy two 250GB drives and mirror
them, or buy two more 80GB drives and get rid of the 9, 36, and 40.

[John Summerfied]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?
Thank you very much,

Apart from comments by others re sizing, trying to use both disks on an
ATA connector at the same time serious hurts performance. As root, try this:

hdparm -t /dev/hda&
hdparm -t /dev/hdb

The ampersand is important.

I imagine you can play games with lvm and create equal-sized virtual
volumes, but again, watch that performance fall off.


You can address the first performance problem by adding ATA disk
controllers on PCI cards.

[Jeff Vian]

Post by Fajar Priyanto
Hi all,
Is it possible to setup a RAID 5 array using different size disks? Such as hda
9GB, hdb 36GB, hdc 40GB, hdd 80GB, hde 80GB.
What are the impact and consequences?

With software raid 5, you can use different size disks.
The requirement is that you create virtual devices (raid partitions) for
use, and all those must be the same size.

For example, the 9gb +36gb +40gb drives could be used to create 9
virtual raid devices of 9gb each and you would have 8 x 9 -> 72gb of
raid array.
This is not necessarily the best way to go since 4 of those virtual raid
devices would be on a single physical device.

However, you could create multiple raid arrays as you suggest and would
still have more than 80gb of unused space with each array spread across
several physical disks..

device 1 9gb on each hda, hdb, hdc, hdd, hde -> 5 X 9gb -> 36gb of
usable space
device 2 27gb on each hdb, hdc, hdd, hde -> 4 x 27gb -> 81gb usable
space.

this would leave about 4gb on hdc and 44gb on each of hdd & hde
unallocated.

Post by Fajar Priyanto
Thank you very much,
--
Fajar Priyanto | Reg'd Linux User #327841 | Linux tutorial
http://linux2.arinet.org
09:36:07 up 1:42, 2.6.14-1.1653_FC4 GNU/Linux
Let's use OpenOffice. http://www.openoffice.org