Topic: Hardware configuration question

[Audrius]

Hello,

I would like to use mirroring capabillity of SME. Is there any difference in connecting HDD: connect both HDD to the same chanel as master and slave or better to connect to different chanels as masters. But on the one chanel will be a CD-ROM whitch may interfer work of HDD? Or not?

Thanks.

[Paul Nesbit]

> I would like to use mirroring capabillity of SME. Is there any
> difference in connecting HDD: connect both HDD to the same chanel
> as master and slave or better to connect to different chanels as
> masters.

Two disks on one channel will mean one IDE controller for two disks; Two disks on two channels will mean two IDE controllers for two disks.  The second option is preferable.

> But on the one chanel will be a CD-ROM whitch may
> interfer work of HDD? Or not?

Not.  It's very common for a CD-ROM and disk drive to share the same IDE channel.

  Paul

[Klaus Eckert]

1) this will be the non-effective way.

2) CDROMs are normaly very slow and do not use DMA.
and the drives are only as fast as the slowest device is.
because of that you will have a slow harddisk.

my hint: try an additional IDE-controller (i.e. PROMISE), connect the second harddisk to it and you will have the best performace.

cheers klaus

[Michael Smith]

Or just attach the CD-ROM for the install & remove it afterwards.  That's what I did for my home server box; it has no optical or floppy drives.  Personally I'm not doing RAID (shame on me!  Maybe next time I order some stuff) but you'll definitely get the best results with each drive on a separate controller.

[Reinhold]

Hi all,

Just a small correction: CD-ROM drives of any half recent make will NOT always slow down the other (mastered) harddisk drive if on the same IDE channel - just try!
Mof on any MS-system it is YOU who slow's the CD-ROM down if you do not allow DMA access to the CD-ROM as well .-)  it's vital when you heavily use your CD/DVD drive for DVD or burning.

TECHbackground: IDE is not able to "release bus" like SCSI.
This is why copying master/slave on one channel(bus) will be slow(er).
Therefore it is advisable to put drives that interact on separate "ide channels". - However on a standard PC there are already two channels/controlers/busses present in the chipset so it is no big deal. No (real) need for new hardware - just make sure that you put your first 2 harddisk drives on different cables. (and make sure those cables are fit for dma .-)

Note: First of all make sure dma is activated in your SME(Linux) system at all.
Afaik SME 5.6 has dma deactivated by default and 6.03 does only auto-activate dma for the 1st hd-drive (at least when I installed).
...HD drives with dma deactivated are really ssssllllooooowwwww.
BTW: There are many other performance options in "hdparm" that may be worth checking.

Regards

[Kelvin]

Just my 2 bits.

I will still avoid sharing a HDD with a CD-ROM drive if at all possible. Firstly, your system chipset must support independent timing in order to support two devices of different transfer modes on the same channel, no matter how new the CD-ROM drive is.

Secondly, HDDs are IDE (or EIDE) devices while CD-ROMs (even the newer ones) are ATAPI devices (ATAPI is a different protocol which uses a much more complicated command structure). This can lead to a performance degradation when sharing the same channel (however, I suspect mostly only when the CD-ROM is in use, though I have not confirmed this).

On SME 5.6 systems, DMA is activated by default if the chipset is a supported one. If the chipset is unknown (like the VIA VT8235), then DMA will not be activated unless you either patch the system or upgrade the kernel.

The other reason for not putting your mirror drives on the same channel is the fact that in certain failure scenarios, if the master drive fails, you will also lose access to the slave drive (not very useful for fault tolerance).

Kelvin

[Reinhold]

Hi Kelvin,

While you do have some valuable points...
The last time I've seen a hard disk that wasn't ATAPI was around the end of the last millenium Remember what (U)dma stands for? - (sorry I couldn't stop myself from replying).

@ALL: just do a

hdparm -i /dev/hdx
... and though will get all the information you need for yourself .-)

Regards

[Kelvin]

Hi Reinhold,

>sorry I couldn't stop myself from replying

Not at all . Don't be sorry. Everyone is entitled to an opinion after all.

As I mentioned in my post, I would not do it, but does not mean everyone else should not.

Cheers,

Kelvin

[Kelvin]

Hi again Reinhold,

Just for informational purposes :

I just reread your post and realised that there's probably a confusion surrounding the use of the terms IDE/EIDE (ATA) and ATAPI.

From what I know, ATAPI only refers to CD-ROM and Tape Drives. Hard disks are actually ATA (or called IDE/EIDE in the old days ...) drives. Ultra DMA drives then translates to Ultra ATA drives.

You could have a look at drive manufacturers' sites (ie. Seagate and Maxtor) and you'll notice that they refer to their drives as ATA drives and not ATAPI drives.

You can even try using the command you suggested :-

hdparm -i /dev/hdx

and you will see your hard disks will list that they are ATA capable (and not ATAPI).

A google search shows lots of people using the term ATAPI with Hard disks. While I am no one in authority over this, I believe that this is an incorrect use of the term ATAPI. Happy to learn otherwise, of course.

Kelvin

[Reinhold]

http://www.google.com/search?q=atapi+history

[Kelvin]

>http://www.google.com/search?q=atapi+history

Yep. And from that document you will see that ATAPI is the standard for CD-ROM and Tapes Drives and continue to be so to the current standard (that's why it's now ATA/ATAPI with ATA being used for Hard disks and ATAPI for the CD-ROM and Tape Drives).

So, in applying to the original post by Audrius, you "could" probably connect the CD-ROM to the same cable as the hard disk. I still would not do it, especially if you are using it for RAID. HDD transfers are *very* badly affected if the CD-ROM is accessed at all (though depending on your server, it might not be very often).

Kelvin