IDE, SCSI and R.A.I.D
Conclusion Who puts a conclusion first ???LOL
First of all I wish to state that I use IDE and that I dont wish to get into any debates over which is better IDE or SCSI . I just wish to state some facts that people dont know about when they argue over this silly issue. IDE is good value for money and with a modern single IDE drive you can get results very similar to a single SCSI drive of the same specs. I'll stress this again, of the SAME SPECS. This changes when adding extra drives...... In some instances a single IDE ATA100 drive can beat a single SCSI drive. Having said that if you can afford it you will always be better off with a 10,000 (or higher as scsi has 20,000 rpm drives now) RPM AV compliant Ultra 2 WIDE (or faster) SCSI drive. The price difference vs the speed benefits for audio recording make scsi not a viable option any more especially when using IDE keeps a lot of traffic off the pci bus. More on that here.
Contents.... What is RAID ?
RAID has been around for years, SCSI is where RAID came from. The research was paid for by the higher price of SCSI drives and also the demand for higher level hard drives. I wont go into much detail over raid here.
IDE RAID uses a intelligent controller that just time shares the bandwidth better between drives while the read/write heads are searching for the correct sector on the disk... Raid is better when using multiple IDE drives for this reason. You wont double your bandwidth when adding a second drive to a raid system although it may give u a 80% increase.
Raid has some problems with audio recording and they are explained here.
Whats the difference ? what does the extra money get you ??? In large sever applications SCSI is always used since 1 hard drive doesn't contain enough storage capacity.. A few years back I got to look at a CRAY at melbournes CSIO atmospheric research labs. A CRAY is a super computer that is very expensive, the model I saw was more than US$1,000,000 and it had 1 GIG of RAM !!! that was in 1998. The hard drives on this CRAY took up half a room with a robotic arm that would pick up the correct hard drive that was needed and place it into the correct bay for reading. The movie "the net" i believe has a scene with this type of hard drive array. SCSI was developed and is still being developed for these applications. SCSI is hot swappable meaning that the drive can be plugged onto the computer while it is turned on and also removed while turned on.
When multiple drives are used SCSI has an edge since it supports parrallel transfers eg. can read and write at the same time, and can acess multiple drives at the same time. These things IDE and IDE raid cannot do. Yes IDE raid can be put in a mode to mirror all data across 2 drives (RAID 1) but it cannot write to both at the exact time, manufactors say it can to make the explaination easier but it cannot (marketing hype).
With IDE only 1 device can be accessed via the IDE controller at a time. So if u have 2 devices on an IDE channel then only 1 can be acesssed by the controller at a time and they can only read or write not both to the same device..... this is where SCSI has advantages and also why IDE RAID has begun to take off..
Adding a 2nd SCSI drive comes close to a 100% increase in total Xfer rate even when not in a RAID setup. When adding a second drive to IDE you get a 30-50% increase in speed due to only 1 device being able to be acessed at once and also the Buffer on IDE device fills up much quicker than SCSI and therefore slows down the transfer from the theorectical values that u get quoted as the transfer rate of the drive. Some benchmarking programs are a joke since they use repetitive data that the systems cache helps out and also some programs dont use large files for testing transfer rates which does get the buffers to fill up which will cause the Xfer rates to drop very quickly. IDE drives are getting larger buffers all the time so this is changing. With SCSI burners you will get less buffer underruns because of the better buffer/cache of SCSI. I can multitask while burning a CD at 8 Speed. SCSI cd burners are not that much more to purchase and are worth every extra dollar.
SCSI is normally a few steps ahead of IDE. EG... at the moment SCSI 10,000 RPM drives have been around for quite some time and IDE 10,000 RPM drives are just about to be released at the time this was written. If you have a IDE drive that has the same Specs as a SCSI drive then the cost vs performance really isn't worth it in a home studio enviroment....If u wish to get low latency then a 10,000 RPM hard drive would definately help u to achieve this and until now SCSI was the only protocol offering this...The RPM of a drive is what determines the ACESS / SEEK times of the drive. The next important value to look at is the AVERAGE SUSTAINED data transfer rate NOT the burst data transfer most drives quote. SCSI is a few steps ahead of IDE with both RPM speeds and sustained transfer rates. SCSI drives are now available in 15,000 and 20,000 RPM models ! That really lowers the acess times of the drive right down. IDE still hasn't really seen any 10,000 RPM models yet.
Things to be aware of with IDE RAID
Without raid you can get 70-80+ tracks of 24bit audio on just one dedicated drive once setup correctly, unless your also recording SuperVHS video then I dont see raid as worth the outlay as you would then need 3 hard drives (one for OS and 2 for audio).
IDE Raid is definately a good idea but I am not convinced that it is reliable for Audio due to the way it "locks the PCI bus" for extended periods of time just like some PCI VIDEO cards where doing a few years back... This locking is called Bus Mastering and its a good thing unless the device locks the PCI bus up for an extended period of time not allowing the AUDIO card to talk to the rest of the computer. Some raid cards have settings that allow u to increase/decrease the length of time that the device is allowed to be bus master, before purchasing a IDE Raid system make sure it has provision to change the PCI BUS MASTERING options. The fastrak/promise/ABIT HODROD raid controllers are apparently really bad for this and if u r serious about raid then u should get a 3Ware Escalade 6000 series controller or similar....remember u get what u pay for. Comparing a fastrack to a 3ware is like comparing a sound blaster to a +$30,000 protools system.
If you own a promise/fastrack controller then....
only connect one drive per channel and dont use maxtor drives...have had known compatablity problems in the past.
use identical drives if setting up your computer in RAID. Dont mix and match drives..
get the utility software from the vendor and disable any PCI BUS MASTERING/ Utilisation options or lower it half way or more.
...if u follow these rules u can get an alright setup. There are heaps of people out there with problems because these cards are so cheap. The fact that you can turn a cheap card into the fastrack with a bios flash and adding a resistor made them very popular. More on the problems with raid can be found here.
want to know more on RAID then click here or visit toms hardware for a simple discription.
if i have written any thing incorrect here and can prove it, not just a different oppinion then please send an email to me and i'll update this info. I try to keep my site as up to date as I can, however the computer world is rapidly changing every day.