SCSI vs Raptor Raid 1

OK here goes...I've wanted SCSI for a while. But I realized something, most hd's are 8ms, raptors are 4ms and raptors in a raid should be 2ms.

So I'm thinking 2 raptors in a raid 1 (mirror) array should give me 8ms write times and 2ms read times. For about $300.

Getting started with SCSI is about $500 so this is the cheaper alternative. What do you think?

I'm not keen on raid 0. I'll take the write performace hit for the redundancy with raid 1.

If anything, your access times (read and write) INCREASE in a RAID configuration

I'd say go SATA Raptor.

But for "Real" securty/redundancy, a RAID-5/6 is what you REALLY want. I consider RAID-1 "Quasi RAID" - especially true if running on an Onboard RAID-1 controller.

I'm eyeing a $500 PCI-e RAID-6 card just for this reason (to have true redundancy that is fairly bulletproof). No need for Raptors here, so I'll load it up with 320GB Seagate Perpendiculars (they can sustain 70MB/s, but with slightly higher access times than a Raptor - and are WAY cheaper per Gig)

SCSI!

Go SCSI, its the only way to get 15k RPM drives, and it's not nearly as confusing as people say.

Wouldn't getting started in SCSI be a whole lot more than $500? For a RAID-1 system?

Is RAID-1 common in SCSI rigs? I thought RAID-5 was pretty much standard for redundancy. RAID-1 just seems inadequate for serious redundancy (and speed) IMO. RAID-5 will have speed AND redundancy.

Anyway, just the SATA RAID-5 Controller Card I was looking at was $500 (a mid-priced card at that), so I don't see how a good SCSI set-up would be $500 including the HD's and all...

Are you running a server, or what? Why do you need 2ms access times? And are you willing to pay out the nose for that small increase in access times opposed to a SATA setup? Food for thought. A good XOR SATA Card and a 4-Drive RAID-5 array should be fairly fast (close to 200MB/s reads and writes from the benches I have seen) and cost less and have more storage than an equivalent SCSI set-up.

A good 4-port SATA XOR RAID-5 Card is about $300, and 4x 320GB Seagate Perp HD's are $89 each. SCSI = $$$$$$$$$$$$$

If I was running a server, I would consider SCSI, but for secure home data backup of irreplacable data, SATA on a good controller should still be more than adequate IMO (with an off-site backup if possible). RAID is really more about the controller IMO - but quick SCSI drives are nice, too (if your wallet is fat enough ).

SCSI can be fast, slow and everything in between, but it's seldom cheap. If it is check your performance, it's probably a lot slower than you think. Used components can be had at a reasonable cost, but expect performance to drop severely.

RAID-5 can have decent reads, but writes are normally much slower. Parity calculations kill performance unless you have a fast controller processor(read expensive) and fast onboard cache RAM.

Other than solid state drives, and I haven't looked at them indepth, you will not ever see a 2ms read time with current drives. The current fastest read access on a disk is the Maxtor 15K II 147GB at 5.5ms including latency. Disk latency alone is in the 2ms range for 15K drives. Typically, there is a slight increase in disk access times using a RAID card(though the Intel matrix RAID does seem to improve them(even that seems to run into a wall at around 6ms)).

RAID-1 is fairly common with SCSI, though it will require a zero channel RAID controller for most onboard solutions or dedicated RAID controller for others.

Things you may not have looked at is PCI/PCI-X/PCI-E bandwidth limitations and workload patterns.

PCI has a net limit of around 115MB/s in the real world. PCI-X is much less common but can have much higher limits on STR. PCI-E is limited by the number of lanes available. Depending on board and mode, this could limit you to potentially as low as 266MB/s theoretical.

Workload patterns can have a large effect on performance. SCSI's firmware is more optimized for server usage patterns and perform worse than SATA in desktop modes. You can see this clearly in this comparison:

http://www.storagereview.com/php/be...&devID_4=264&devID_5=323&devID_6=322&devCnt=7

These are all high capacity, high performance drives. Yet, in terms of high IO load, the SCSI drives consistently out perform the SATA drives. In the more typical patterns for desktop users, SATA, even 7200RPM, performs well and often exceeds SCSI's performance at a much lower cost. The Seagate Barracuda ES is the enterprise version of the 7200.10.

Personally, the SATA offerings make more sense from a cost benefit standpoint for most non server uses.