Software RAID which one mdadm or mkraid

kernel99 · 09-17-2008, 12:40 AM

i'm in a process of building software RAID in centOS. i'm in a learning phase currently.
i used mdadm inorder to create different RAID successfully.
i could fail the drive and add in.

is mdadm is more useful than mkraid?

also if i would like to create multiple raids and combine one should i use assembly mode in mdadm?
in general practice is it good to combine two or more raid levels in one....
ifnot in which case is it more useful combining two or more raids.

would be glad to hear.

thanks
kernel99

kenneho · 09-17-2008, 09:38 AM

Quote:

Originally Posted by kernel99

i'm in a process of building software RAID in centOS. i'm in a learning phase currently.
i used mdadm inorder to create different RAID successfully.
i could fail the drive and add in.

is mdadm is more useful than mkraid?

also if i would like to create multiple raids and combine one should i use assembly mode in mdadm?
in general practice is it good to combine two or more raid levels in one....
ifnot in which case is it more useful combining two or more raids.

would be glad to hear.

thanks
kernel99

I've attended some Red Hat training, and they focus on mdadm. I'm sure this didn't answer you question, but hopefully it was of some help.

Bruce Hill · 09-17-2008, 05:36 PM

Quote:

Originally Posted by kernel99

also if i would like to create multiple raids and combine one should i use assembly mode in mdadm?
in general practice is it good to combine two or more raid levels in one....
ifnot in which case is it more useful combining two or more raids.

would be glad to hear.

thanks
kernel99

Maybe I'm not understanding your question, but here's my little experience.

My distro doesn't even have mkraid, so I never considered it. And this is the
first I've heard of assembly mode in mdadm, so I obviously didn't use it.

When I did some research into RAID in Linux, the choices I read about were
software RAID versus hardware RAID. For the purpose of this RAID (just my
personal desktop machine), I didn't care to spend a lot of money on extra
hardware. Plus, my ~/ and all extra software and kernels I build are backed
up every night. So there's really nothing I'm risking.

If I were to build RAID for a mission critical server, I'd definitely buy
the much more expensive hardware and SCSI disks.

I'm also not sure what you mean by "combine two or more RAID levels in one?"
So here's a glance at my RAID, in case it sheds any light. And also, if a
wiser man than I sees something amiss, he can enlighten me.

Code:

RAID1 - /dev/md0 - swap
RAID1 - /dev/md1 - /boot
RAID0 - /dev/md2 - LVM encrypted with LUKS containing / and ~/

Code:

mingdao@silas:~$ sudo /sbin/fdisk -l

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x681acfcf

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1         122      979933+  fd  Linux raid autodetect
/dev/sda2             123         134       96390   fd  Linux raid autodetect
/dev/sda3             135       12292    97659135   fd  Linux raid autodetect

Disk /dev/sdb: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x18142ccc

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1         122      979933+  fd  Linux raid autodetect
/dev/sdb2             123         134       96390   fd  Linux raid autodetect
/dev/sdb3             135       12292    97659135   fd  Linux raid autodetect

Disk /dev/md0: 1003 MB, 1003356160 bytes
2 heads, 4 sectors/track, 244960 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn't contain a valid partition table

Disk /dev/md1: 98 MB, 98631680 bytes
2 heads, 4 sectors/track, 24080 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md1 doesn't contain a valid partition table

Disk /dev/md2: 200.0 GB, 200005648384 bytes
2 heads, 4 sectors/track, 48829504 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x08040000

Disk /dev/md2 doesn't contain a valid partition table

mostlyharmless · 09-17-2008, 05:50 PM

mdadm is usually recommended. mkraid is the older raidtools command.
The assemble command is used to build arrays,and there is no problem using "matrix raid" 1+0, or 1+1 or whatever it is you desire.

Quote:

i could fail the drive and add in.

Sounds like you want data redundancy, not speed, so you want RAID 1 or 5 not 0. I'd recommend reading up on RAID in general - there are a lot of threads on the subject here as well as on tldp.