Topic: Software raid 1 mirroring questions

[mark]

Hello,
I am thinking about converting my server over to a mirrored drive config
and have a few questions that hopefully some people that have done this
or have experience with it may be able to answer. I've searched the forums
a bit and read the online manual but haven't found much detailing raid 1
other than the fact that it is avail. and how to choose it during an install.

1. will using software raid 1 impact the server performance negetively?
    The server in question is a 400Mhz celeron w/ 384Mb ram.
    the mirroring will be done on two 7200rpm 15Gb ATA/66 disks. There
    will also be an ide cdrom as a primary slave with the possibilty of adding
    a single non-mirrored disk as the other slave for an i-bay of noncritial files.
    the load is fairly light only about 7 client boxes on the lan w/ occasional
    webmail usage. (usually only 2-3 active clients on at once). The data is
    fairly static on the box. Mostly data/web pages are written to the box
    just once and most of the work is just accessing the web server externally
    or pulling files off an i-bay internally. Not much writing activity.
2. The manual states in chap. 6 that "Should the primary disk experience a
    hardware failure, the mirror disk will continue operations as if nothing
    had happened." This sounds like a root disk failure will not cause any
    service interuption it will just fail over to the remaining/working mirror.
    Is this correct? Do I just need to keep an eye on the logs to see if there was
    a failure or is there a raid status section in the server-admin if you
    are running raid 1? Or is there some other type of notification method used?
3. In the case of a drive failure what is the recovery procedure?
    Is it as simple as replacing the failed drive and power cycling?
    Or are there some commands that need to be run to recreate the
    mirror and sync up the data?

Is there anything else that I should watch out for. Tips or gotchas that
others have encountered?

Thanks for any info/guidance provided.
-Mark

[Tony Olesen]

First. Dont add anything as slave to your HDD-controller - It WILL slow performance... Get a second IDE-controller for your CD-ROM.

Second. Darrel May has written a very nice RAID1 HowTo, that answers your questions about monitoring and recovery. It can be found at:

http://myezserver.com/docs/mitel/raid-monitor-howto.html

I can recommend http://myezserver.com/docs/mitel/
It has several good HowTos.

Your performance should not suffer from RAID1 (Unless you add a CD-ROM as slave), actually reading could be a little faster depending on how the RAID1 is construction... (It is possible to READ from both drives simultaniusly in RAID1, but i am unsure if that is done by linux).

Regards

Tony

[Alexander Ziemann]

Hi,

i have a pretty similar conifg (400 mhz PII, 256 MB RAM, 2* 18 GB SCSI Disks) and the read performance improved after installing raid 1. I did not measure or compare. But you can "feel" it. Also Raid1 on e-smith is faster than raid 1 on NT4 Server. Only writing large files is slower.

If the files do not change to often and you have a good backup-device, i perhaps would not use raid1. It is more costly. And failure of a harddisk is not to often.

I need raid1 for heavy changing data. Backup alone will not do with that.

alex