RAID Question (1 Viewer)

[Cameron_Peck]

I want to make a “large hard drive” out of multiple hard drives. I would like to be able to add to this “large hard drive” in the future. I have an Asus A7N8X Deluxe motherboard that supports RAID 0 & RAID 1 with serial ATA drives. I am confused as to what these (RAID 0&1) do. Is a SCSI array the same as using RAID with SCSI drives? I am building a HTPC and the drive I have now is 11GB so it is time to get new drives. I want to make sure that I get the correct stuff. I don’t want to buy a 120GB hard drive and find out latter that I cannot expand it without adding another drive letter. Please excuse my ignorance. And thanks for your input.

 

[John_Berger]

RAID 0 is striping.
Benefit: All drives in the stripe are seen as one drive.
Drawback: Failure in one drive means a failure of the stripe.

RAID 1 is mirrioring.
Benefit: Up to 50% of drives in the mirror can fail without problem
Drawback: You lose 50% of total possible capacity for the mirror

I don’t want to buy a 120GB hard drive and find out latter that I cannot expand it without adding another drive letter.

My God, man! What do you plan on doing that makes to think that 120 GB won't be enough?!

 

[Cameron_Peck]

I will be putting my music collection on the PC. And I will be using it like a TIVO unit also. I know that it will be enough for now, but when HDTV is mainstream I’m sure that 120GB will be inadequate. Four years ago my 11GB hard drive was “more than enough”. Of course four years from now I will probably be able to buy a 2000GB drive for what 120GB costs today.

 

[John_Berger]

Heh. One year from now you'll probably be able to buy it.

 

[Ammon]

Tivo announced that they are coming out with an HDTV recorder possibly the end of this year. Whats the advantages of using the PC as a PVR as compared to a Tivo? I currently have a Tivo, and with all the options I have, plus a handy remote. I paid $75 for my 35 hour Tivo, and with the ability to upgrade it myself for longer recording hours, why would a Home PC work better? Just wondering, mainly because I've never looked into it before.

I remember when I bought my first "BIG" HDD. 250mb. And it was a sweet deal at $350. I was fed up with my 20mb drive. I could install Doom and Wolfenstein, but man, it took up too much room!

 

[Cameron_Peck]

I have a Pronto remote, but I still use the Tivo remote for all of my Tivoing. It is by far the best remote I have used before.

 

[Danny R]

Many RAID controllers do have JBOD (Just a Bunch Of Drives) mode, which allows you to merge additional drives together so that they all appear as one big one. It depends on the controller/OS if you have to reformat the original drive or not before adding a new one. There is also no fault tolerance, and speed is the same as if you had one drive.

Also many OS's have software RAID built in as well, which can be set up to perform much the same was as a JBOD controller.

If you are having a bunch of drives working together as one unit, I'd put them in a RAID 5 array. With it, should one drive fail your data can be restored from the parity information stored on the remaining drives. Your speed is increased because you are writing to all drives simultaneously, but you do take a small hit in storage capacity, as a portion of the combined drive size has to be used for the parity info.

Is a SCSI array the same as using RAID with SCSI drives?

Yup, RAID can work with either SCSI drives or IDE, depending on your adaptor of course.

 

[Hanson]

You can archive PC recordings. You can convert them to avi files or whatnot. You can stuff a DVD player into a PC. You can buy now.

The HD Tivo as it was shown has the same limitation as MyHD -- it cannot record and play at the same time. No price or recording size set yet. Or release date.

MyHD and HiDTV both come with remotes, but they are limited. You'll still have to use mouse and keyboard for lots of stuff.

BTW, if how many RAID channels do you have on the mobo (I assume just 2 because you can only do RAID 0 or 1)? If there are only two and you have to master/slave to get four disks, it really negates most of the performance gain. If you want RAID5, get a RAID card with 4 channels.

 

[Wayne Bundrick]

It isn't easy to expand RAID and only the very newest and most expensive RAID stuff make it even slightly convenient.

The NTFS in Windows 2000 and XP Pro have the ability to mount an entire drive as a folder located on another drive. It could be possible to reach every file on every hard drive on your computer from "C:". Application software will not know that the files are not really in a folder on drive C. Powerful stuff and convenient for expanding storage with little disturbance to existing files and applications. Of course, this sort of thing has been a part of Unix and for decades.

 

[John_Berger]

Of course, this sort of thing has been a part of Unix and for decades.

{ whistling innocently } I wasn't going there.

 

[Danny R]

The HD Tivo as it was shown has the same limitation as MyHD -- it cannot record and play at the same time. No price or recording size set yet. Or release date.

Dish will release the 921 sometime this summer supposedly.

While the Dish recorders don't have name based recording like the Tivo's, the 921 should be able to record two HD sources simultaneously while playing a prerecorded third HD source. Likewise it can record over the air sources.

 

[Hanson]

You know, I was reading the specs on Dish 921. It sounded like you could record HD and Analog at the same time, but it didn't sound like it could handle 2 HD streams. If it does, I assume you would need to have Dish Network (1 Dish stream, one OTA antenna).

How do they fit 50 hours of HD programming on a 250 GB HD? The HD stream is 9GB/hour.

 

[Wayne Bundrick]

No slam on Microsoft intended, other than that it took them long enough to figure it out.

On the other hand, they did have the exact opposite with the SUBST command in MS-DOS.

 

[Cameron_Peck]

It sounds like I want a RAID controller that supports JBOD. Thanks for your help.

 

[Scott H]

My God, man! What do you plan on doing that makes to think that 120 GB won't be enough?!

Internally my G4 has three 120GB and a 60GB Two of the 120s make up a 240GB RAID 0 array. All are Western Digital SEs.

Incidentally, our ReplayTV will be on our wireless network as soon as a software update activates the USB port. Besides access to the net shows can be transmitted to the Mac and burned to DVD.

 

[DonRoeber]

Er... no, JBOD is just that... Just A Bunch of Disks. It really means no RAID at all. If you want to present your disks as one big one to the operating system, you've got a few choices.... but JBOD isn't one of them.

RAID 0 = take two hard disks, and "stripe" them. This shows the OS that you have one drive, but the RAID controller actually is writing data across the two hard disks. This can increase performance, because you essentially have double the availble mechanics for reading and writing. Of course, you're not going to get 2x the performance, because you'll run into situations where both blocks of data that you need will be on one disk. But it helps.

RAID 1 = take two hard disks, and mirror them. The RAID controller shows the OS that you have one drive. The controller is writing the same information to both disks. No performance gain, and no capacity gain either. But if one of the disks in the RAID fails, you're not up a creek.

RAID 0+1 = take 4 hard disks. Create two RAID 0 disk sets, and mirror them. This is pretty cool; now you've got great performance, big disks, and redundancy. Of course, you're buying four disks and getting the capacity of two, but you'll be okay even if two disks die. The OS will see one disk available to it.

RAID 5 = take 4 hard disks. Spread data across three disks, write parity information to the fourth. Any one of these disks can die, and you'll be okay. You also get 75% of your total raw disk capacity presented to the OS. This is probably ideal, but it's not as fast as RAID 0+1, since the RAID controller needs to do lots of extra work to compute parity.

JBOD = take as many disks as you want, and hook 'em up to the RAID controller. The RAID controller shows the OS each disk that you have connected to it, and doesn't do anything to prevent data loss, increase performance, or anything like that. Essentially, you're using your expensive RAID controller as a half as expensive disk controller.

 

[Tekara]

I'm going to jump in here.

DonRoeber: your description of raid5 is actually more of a description of raid7. raid5 is similar but the parity information is actually striped across all the discs (no disc will carry it's own parity information). thus there is no need for a seperate parity drive. here's some information for you if you are interested in the other estranged raid methods: http://www.acnc.com/04_01_05.html

striping is not a raid per say as there is no redundancy in a stripe but it's accepted as a raid for the sake of things.

I use raid 0 on my asus a7n8x by means of sata->pata adapters. the drives of choice are a pair of wd800JB's they work wonderfully. just make sure you have a disc with the drivers for the sata controller on it so that windows can recognize the hdd when it's installing.

 

[Danny R]

Er... no, JBOD is just that... Just A Bunch of Disks. It really means no RAID at all. If you want to present your disks as one big one to the operating system, you've got a few choices.... but JBOD isn't one of them.


I think your adaptor must not have implemented it properly then. I've definately used this for simple spanning and combining disks.

From the Adaptec website: JBOD: An acronym for "Just a Bunch Of Disks". It represents a logical volume that is created by the concatenation of the partitions on one or more disks. This is perhaps one of the most elementary forms of an array.

 

[John_Berger]

Actually, Don's definition is correct -- Adaptec's definition is not. I know that this is one of the things that they're experts in so we expect them to know exactly what they're saying; however, that doesn't mean that they're infallible.

JBOD is the term for an group of disks that does not have a hardware RAID controller managing it but is expected to be a part of an array. (This is probably why Adaptec phrased their definition as they did.)

For example, the Sun Microsystems A1000 uses a hardware RAID board that is built into the array case. This array manages the disks and requires the use of separate software to control the array controller. Because this device uses a hardware array manager to control the disks and therefore the disks will not be managed directly by the operating system, it does not qualify for JBOD.

In contrast, the Sun Microsystems D1000 is the exact same thing but without the hardware array controller. When connected to the server, the operating system sees every disk individually and can control each of them individually. It is assumed that the D1000 was purchased for an array; however, it is not required. By definition, this makes the D1000 qualify for the JBOD label because each disk is directly identified and controlled by the operating system.

Now, going by that terminology, any motherboard that has a RAID controller on it does not qualify for JBOD because it has hardware built into it to manage the RAID disks.

I hope this clears stuff up for some.