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Need help on Tape,Optical disk...
Hi,
Right now we are looking for the relaibility study of the disk, tape, magneto-optic disk etc. which are primarily involve in the mass storage. Our requirement is any of the tape or above device data to predict the relaibility. I'll deeply appriciate if anyone can help me out to get the data or pointer. Thanks & Regds, Babi |
#2
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Need help on Tape,Optical disk...
On 14 May 2006 23:45:15 -0700, "babi" wrote:
Hi, Right now we are looking for the relaibility study of the disk, tape, magneto-optic disk etc. which are primarily involve in the mass storage. Our requirement is any of the tape or above device data to predict the relaibility. I'll deeply appriciate if anyone can help me out to get the data or pointer. Thanks & Regds, Babi Well, I believe plenty of studies have been done that show tape and optical are more reliable than disk. However, it's alot simpler to put disk in a raid and make the overall architecure much more reliable. But from a pure media viewpoint disk is the least reliable of the 3. ~F |
#3
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Need help on Tape,Optical disk...
Not sure if I agree with everything Faeandar said, but I do agree in
part. The big advantage that disks have over tape or optical is that you can put them in a RAID array to essentially remove any concerns about reliability. No longer will the loss of a single piece of media cause your storage process to fail. I don't share Faeandar's opinion that tapes and optical are far more reliable than disks. While I don't have a lot of experience with optical, I do have extensive experience with both disk and tape in many people's environments. If disks failed anywhere as often as tapes do, most people I know would throw them out. My personal opinion is that this unreliability comes from two things. The first is the fact that tape (and optical) systems are open systems, where the media must be injected and ejected from the drive, introducing contaminants each time. Disk drives, on the other hand, are closed systems -- no contaminants ever. In addition, the physical media of tape (and some optical) is inherently more "wimpy" than the media used in a disk drive. Disks can also handle more g-forces than most tape cartridges I use on a regular basis. Drop a DLT or LTO cartridge from shoulder-height, and you can expect some parts to come flying off inside. In comparison, a powered-off disk drive could handle a similar fall much easier. Now... Power off a disk drive and set it on a shelf next to an ejected tape drive and leave it there for five years. I'll trust the tape every time in that scenario, as disks were not intended to be left powered off that long with data. The second reason that tape is less reliable is that people don't stream their tape drives. They're sending 5 MB/s to a 60 MB/s drive, or 10 MB/s to a 150 MB/s tape drive. The thing's constantly stopping and starting, going into drive, then reverse, then drive, then reverse. You do this enough, and you'll fail too. In contrast, disk drives can go any speed you want them to. You want 150 MB/s? Fine. You want 1 KB/s? That's fine, too. Tape drives can't say that. The result is really unreliable tape drives. The proof's in the pudding. I've watched company after company convert from tape to disk for backups, and they've watched their success rates skyrocket. Is that because tapes were less reliable, or just because disk is a better match for how backups behave? Either way, in a real-world scenario, disks trump -- and disks in a RAID array trump even further. Now, as to optical, I don't have any data. I'm all about backups, and people just don't use optical for backups -- the transfer rates simply aren't high enough. I think we've finally reached double digits with some of the formats, but the numbers are still way behind those of tape or disk. However, if I had to store something on a media that I was going to store for 7+ years, I'd use optical in a heartbeat. |
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