Topic: SCSI raid

[Dennis]

Hello all,

I would like to use 4 scsi harddisks for my sme server 6b3.
During the installation i can only choose mirror or single harddisk setup.
I would like to make a raid-5 setup so i have tripple the capacitie with fault tollerance.

Is this possible to configure?

[Dan Brown]

Possible, yes, software RAID 5 has been available in Linux for quite some time.  Easy?  Depends on your skill level; I wouldn't know how to do it, but the howtos at linuxdoc.org would be a starting point.  Recommended?  I wouldn't think so--the parity calculations take a lot of CPU overhead.  Use a hardware RAID controller instead.

[Dennis]

Thanks,

I didn't think about the CPU overhead. I think i drop the idee to use software raid.
The hardware raid controller is indeed a good choice but i can't afford it right now.

[Alexander Ziemann]

Hi,

just buy yourself an old UW-SCSI RAID Controller Mylex 960 Series at Ebay or somewhere else.

Works nicely - good performance and you can use your new/old SCSI disks. I am very happy with mine and it costed 11 EUR plus PP.

az

[Reinhold]

Dennis,

I'm hard pressed that famous Dan Brown thinks software Raid is that hard to do ... ... actually what you "simply" do is:
(1) partition some disks - as usual
(2) write a text file called "/etc/raidtab" arranging those drives as a new (raid-) drive
(3) activate that newly described array "md0": mkraid -f /dev/md0
(4) format that new "raiddrive" mke2fs /dev/md0  or better mkfs.ext3 /dev/md0

... and look at what it does (sync,ok,drive bad) with: cat /proc/mdstat
...SME 6.0 kernel is autoraidstarting at boot so raidstart /dev/md0 isn't even needed
... and you can just put that new "/dev/md0" drive into /etc/fstab

SPEED? Agreed if you recycle that old 233MHz I wouldn't do it .-) but at home I put 5 older 80GB IDE's as file dump into an older PIII 550 ... and even this it is quite able to fill the 100Mbit Net at 6-7 Mbyte/s write and 7-8 MByte read ...

OTOH:
- you won't have "tripple" capacity but just 3/4th of what your single HDs give (n-1)
- you will have a hard time if you want to boot from the raid - Dan is absolutely right in that (I would even consider it asking for trouble .-)
- that Mylex controller setup of Mr. Zieman might be just best price/performance if you need local HD speed
BUT: those probably old scsi uw-scsi-disks are smaller&slower than any new  Ultra100/133-50MByte/s-8MByte-cache-IDE-Harddisk ...for a mere 100bucks .-/

Reinhold

[Alexander Ziemann]

Hi, Reinhold,

my "probably old scsi disks" are 2 year old IBM DYS U160 and 18 GB HDs; they are still quite expensive (about 150 ¤ pcs.) but they are there....

Because i do like to boot from the raid-disks and i do not like 3 - 5 HDs in an entry-level server i would by all means stick with HW-Raid.

az

P.S: I do not like to hand-write fstab also, because i am part-time admin and the server has to be up and running all the time....

[Reinhold]

Alexander,

... beware: the rest is mostly my opinion and my experience = not helpful maybe

How far does a 18Gb HD file server get you in 2003?
It's two movies to work on in that np-group I help out or 4 serious gameinstalls for your kids

Seriously - 80Gb 50MB/s 8Mb/cache IDE is 65 euros (?) (can't read your char) as of today...
...now you really believe that your "U160" is fast-er ??  ---> buy RAM that's fast.
...nothing to say about "over a 100Mbit net" ??? ---> this will slow everything to 8MB/s

In my opinion  (imo) it is much safer to put the system on a separate disk - not just a separate partition - I'd be glad to explain why )))
(...basically it boils down to "old harddisks die" )

3-6 HDs in an entry level server are a problem ???
Then why not buy ONE fast & cheap 200Gb IDE HD in the first place ???
...back it up with a 2nd mirror-Raid if you want (IDE works out of the box with SME 6.x) - ...however I really thought we are (all) on "recycle" here

And on "hand writing fstab" :
Who do you think writes fstab in 90% of all Linux installs
Seriously - if you'd have said "raidtab" maybe, but fstab is imo basic knowledge if you intend to expand your Linux system yourself.

Don't get me wrong ... my hands are/were sweating too when I wrote "the" fstab the first few times - but as a sysadmin imo you SHOULD get some training here .-) ...what will you do if it breaks ??? - Your system will go to readonly after boot and you are in serious trouble then ... (to comfort you: SME is very easy to handle then... unlike Suse for instance .-)
What happens if your old/new controller fails ? or your old scsi HD?
i) you cannot fix it ii) you cannot buy a new one iii) you are back to backups ... and (most likely) a newly set up box .-)

Part-time admin?  Great! I guess that's true for you & me & 2/3 of all members here. - Thats why we came to SME I believe .-)

Reinhold

[Brent]

Dennis,

I'm using SME 6.0b2 right now with 5 SCSI disks in a RAID5 hot swap array using a Compaq SmartArray 221 hardware controller.  Upon install, I just set SME as if I was doing a single disk installation and let the hardware do the "RAID" part.  The controller was an extra $70 (CDN.) and IMHO well worth the money.

It's worked quite well and I've had no problems to date.  Processing wouldn't have been a problem for me as I'm running this in a quad processor (4xP111 500) machine, but for simplicity's sake, it was much easier to use the hardware RAID controller.

Also, since I don't have a tape drive in this machine for backups, I wanted the redundancy of the RAID5.  My primary means of backup is a RH box on the network with a burner in it

As for file space, it depends on what you're doing with your box.  Mine is primarily a small website hosting/email provider, so my SCSI drives are only 4.3GB each (and were $14 CDN new bulk!), but that gives me over 16GB of drive space - which is plenty for the handful of sites I'm hosting.   I don't use my server for personal storage - it's strictly a "business" machine.

If the RAID is important enough, a hardware controller is definitely something you don't want to skimp on.  Check out www.itxchange.com for a good source of used/refurb/new bulk hardware components, and you'll likely find what you're looking for there.  They've always had what I needed, shipped fast, and packed extremely well.

[Alexander Ziemann]

> How far does a 18Gb HD file server get you in 2003?

Extremely far, as long as video, gaming and such stuff stays off the server. We are running a 10 Person Office here with tree printers, about 2 GB databases for accounting, appx. 3000 text-files created and printed every year and this with old data from more than 10 years office-life. And this was (now it changed to IDE disks) all on one mirrored 18 GB SCSI - complete data was (and is) about 6 GB, 2 of which are plain apps and static data. Plus 2-4 Websites and tons of mail we are receiving.

> It's two movies to work on in that np-group I help out or 4
> serious gameinstalls for your kids

OK - we have no games and such stuff here. Even at our home-server. That one is running on an old P I/233 and 9 GB SCSI btw.

> ...now you really believe that your "U160" is fast-er ??

It does not matter. Bottleneck ist the network. And seek/read times in a HW-Raid with "old" disks are very comfortable - not slower than new IDE-drives with our Promise TX2000 controller.

> In my opinion  (imo) it is much safer to put the system on a
> separate disk - not just a separate

It is safe to do backups and know how to restore them ; in my pretty long server-life i had two serious disk-crashes.

And now i change server-disks every two years and never had trouble again. BTW: The "old" SCSI-drives have MTBF twice to four times longer than normal "new" IDE drives.

> Then why not buy ONE fast & cheap 200Gb IDE HD in the first

My work and i am done with about 10 GB filespace. That is why.

> imo basic knowledge if you intend to expand your Linux system
> yourself.

I am a working professional, not a tuning freak. I have no need to "expand" my linux system. And sweat should stay with sports
 
> Don't get me wrong ... my hands are/were sweating too when I

> What happens if your old/new controller fails ? or your old
> scsi HD?

If hardware fails i replace it. I take my backups and build a new system. About 2 hours alltogether.

But i never have seen a Controller-Card die And i have RAID1 - so what?

For serious: I think we are just going different ways to different destinations - you are demanding another server-environment than i am.

az

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