RLES 3 - Questions on S/W RAID

[Lee Eng Huat]

Hi,

With regard to S/W RAID capability in RLES 3, I've the following questions:

1) How many RAID 1 disk members could it supports?
2) Could it supports RAID 1 volumes across two external fibre channel (FC) disk arrays?
3) What is the maximum distance could it supports RAID 1 from the host to the external disk arrays, connected thru' FC as mentioned in 2) above?
4) Can a mirrored member be add or split online without disrupting system operations?

Would appreciate advice on the above.


Thanks,

Lee Eng Huat
Mobile: +65 94371226

[Slawomir Gora]

Hi,

you have to use raidtools for software raid,
LVM on linux does not support raid 1.

2) yes
3) It is not software limit but hardware
For FC (2Gb/s - 300m) (1Gb - 500m)

look at:
http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html

[Johannes Krackowizer_1 · Accepted solution]

hi Lee Eng Huat,

1) currently 12 disks (mirrors + spare disks) but in experimental patches this limit is 256 disks.

2) you could create software raid on two devices it's no matter if they are both in the machine or outside or one is ide and one is scsi, no matter all combination should work. you should also be able to create a file partition it with fdisk and use the /virtual partitions in the file to make softwareraids (i have tested this configuration about 1 year ago).

3)this is only a hardwarelimit i think ide is 40 or 60cm, scsi se 1.5m to 6m, scsi lvd 12m, scsi hvd 25m, FC 300-500m

4) there are two commands to add or remove disks in a raid array: raidhotadd, raidhotremove
to start or stop raiddevices (the whole md device) raidstart, raidstop

best regards,

johannes

[Lee Eng Huat]

Hi Johannes,

Are these (1 & 4) stated in any of Redhat documentation where I could refer for more details?

Thanks,

Eng Huat

[Johannes Krackowizer_1]

Hi Lee Eng Huat,

sorry i don't know about any redhat specific manuals and howtos but i know this:

@1 look at "man raidtab"
@4 http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html
at Chapter 8 you learn howto reinsert a "faild" disk into an existing array.

or have a look at Chapter 6.3 simulate a drive fault and reinsert the drive.

but please read the hole howto to understand how software raid works and get a computer where you can test your settings without losing any important data!

best regards,

johannes