Topic: RAID

[Mark Allison]

I'm looking at building a new server and I was wondering, is the software raid that's available during the Install vary fast? and would a hardware raid be a better choice, even on a small server?

Thanks,
Mark

[Kelvin]

Hi Mark,

Note : The following is a personal opinion only.

If you don't want any hassles in the event of a drive failure, consider hardware RAID. If you get one that supports hotswap as well, it can be a real life saver, especially if you can't get on site but the client (or you) may have a spare hdd on standby already.

A quick search through these forums will bring up a number of postings from me and others on the relatives merits of both.

Cheers,

Kelvin

[Alejandro]

Software raid is a cost effective acceptable solution but is always slower than hardware raid.
If you plan to install a software raid, and you want to keep it cost effective, you should get uata 133 capable hardware (motherboard cables etc) and fast drives (ej two identical 7200 rpm uata 133 hdd) to obtain the best perfomance, but it will be slower (and cheaper) than hardware raid, wich as a counterpart is safer and more reliable.(in this case you can choose between different technologies (ide or scsi) and between mirror, or stripping raid or a combination of both, it all depends on relation between the money you are able to spend and the speed and reliability you will get for that money.
(this is just my opinion)
BTW: I have a software raid server, but my saved money went somewere else
A

[Charlie Brady]

Alejandro wrote:

> Software raid is a cost effective acceptable solution but is
> always slower than hardware raid.

Do you have any evidence to back that up that assertion? It's my understanding that all raid is software RAID, and it's only a matter of where the software is implemented, and how well it is implemented. I don't know of any physical reason that it need be slower.

> If you plan to install a software raid, and you want to keep
> it cost effective, you should get uata 133 capable hardware
> (motherboard cables etc) and fast drives (ej two identical
> 7200 rpm uata 133 hdd) to obtain the best perfomance, but it
> will be slower (and cheaper) than hardware raid, wich as a
> counterpart is safer and more reliable.

Again, without hard data, you shouldn't claim that either is safer or more reliable.

The rest of your comments are certainly valid.

Comments here might interest you:

http://www.matrixlist.com/pipermail/pc_support/2001-September/000032.html
http://www.linuxquestions.org/questions/archive/18/2003/01/3/41463

> BTW: I have a software raid server, but my saved money went
> somewere else

Tape backup would be one good choice.

Charlie

[dave]

Software RAID would very likely work fine but before you commit to it, check on these boards for questions related to recovering/rebuilding the mirror if you have to replace a failed drive.  I have no direct experience with recovering a failed software mirror but from what I gather, it can be problematic.  

I've used IDE and SCSI RAID cards under various OS's and I've always had the best luck with SCSI hardware RAID.  Most SCSI RAID bios will include not only the initial RAID setup but recovery/rebuild functionality.  Many SCSI raid cards will also allow expanding an array, creating multiple arrays and don't have the 2 drive per cable limit IDE does (actually, to do IDE correctly, you should only have one drive on each cable which creates a 1 drive/cable limit).  Plus, in hardware RAID, you define the array and the hardware bios presents the entire array to whatever OS you're installing as a single device.  SCSI can definitely be more (usually MUCH more) expensive than similar capacity IDE devices but I end up replacing IDE drives about 3 times more often than my SCSI hdwe.

Just my (somewhat educated) opinion, others will say differently...  Good luck with whatever you decide to do.

[Kelvin]

If it all gets a bit much, and if you have the budget for it, consider self contained subsystems like the Accusys 7500 :-

http://www.quasarsoft.com.au/hardware/index.php?topic=storage

OS independent (no drivers needed to run this unit as long as your operating system supports your motherboard's onboard IDE controller or whichever IDE controller you connect this unit to), hot swap capable, auto rebuild with built in battery backup to track rebuild status, audible alarm. Only thing it lacks is a means to tell the OS a drive has failed, so if a drive fails when there is no one around, nobody will hear the alarm. You could even take an existing IDE based installation of SME and give it an instant RAID 1 upgrade without reformatting / reinstalling !

As for the reliability of IDE drives,  I have personally not found SCSI to be any more reliable than IDE. After all, even on the 3 year old Compaq Servers I manage, their SCSI drives die as well while my other 2 8 year old Netware servers using IDE drives never had a drive replaced (on this note, let me be the first to say that they don't make hard disks like they used to ! - SCSI or IDE !). It is also a lot easier to pick up a replacement IDE drive than a replacement SCSI drive in a pinch. Unless your server is under heavy access load, in which case SCSI has an advantage, IDE drives would do just fine.

Kelvin

[Boris]

Beware that Accusys 7500 not LBA-48 capable, max drive size 137Gb. ;-(

[Kelvin]

>Beware that Accusys 7500 not LBA-48 capable, max drive size 137Gb. ;-(

Then go for the 7500's bigger brother -> the 7630 which is RAID 5 capable supporting 3 drives in the one unit. This is actually an old problem dating back to old SCSI based RAID systems as well.

What you lose with the 7630 over other hardware RAID 5 controllers is the single channel through which data flows (the single cable connecting the motherboard to the 7630).

In any case, have you asked if a later firmware is available for your ACS 7500 which does support LBA-48 drives ?

Kelvin

[Guck Puppy]

Kelvin wrote:
> In any case, have you asked if a later firmware is available
> for your ACS 7500 which does support LBA-48 drives ?

Don't you sell 'em? Do you know if such firware exists?

[Kelvin]

>Don't you sell 'em? Do you know if such firware exists?

The problem is my distributor actually relies on me for a lot of the feedback with regards to problems with the ACS7500 (as I use a lot of it ). However, to date, I've not had to sell any hard disk larger than 80 GB (as I mainly deal with servers and small businesses. 80 GB is a lot of space for most of my clients - many have operations with 10 or less PCs). So I have not personally come across a large enough hard disk to test the limits of the ACS 7500.

I asked the distributor some time back but have not got a reply. Distributors in other countries might be more forthcoming with an answer so it stands to reason if I actually put it forth to other users possibly from other countries, their resellers / distributors might actually tell them. Then I could actually put pressure on my distributor to get me an update. Attempts to contact Taiwan directly never gets a reply.

A while back I also discovered the ACS 7500 does not work with the newer range of Seagate Barracuda (and possibly others) drives (the older Barracuda's - no problem). After much phone calls, and experimentation on both my part and the distributor's, they finally approached Accusys in Taiwan who then sent us an updated firmware which fixes the compatibility problem.

Kelvin

[Guck Puppy]

There's been a recent slashdot post about Raid mirroring controllers :
http://ask.slashdot.org/article.pl/08/28/2143208&mode=nested&tid=137&tid=198

[Guck Puppy]

Also, this very thorough guide to HDDs and RAID stuff :
http://www.storagereview.com/guide2000/ref/hdd/

[Kelvin]

Hi All,

It's amazing what a few carefully worded e-mails can get you .

The definitive word on the ACS-7500 :-

Older batches cannot support LBA48 drives. The newer ones can. The only way to tell is to check that the box says it supports large drives.

Its sister product, the ACS-7630 which is a similar product but RAID-5 capable, can support LBA48 drives with a firmware upgrade.

Kelvin