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WD's Monster 2TB Caviar Green Drive, Preview Test
MojoKid writes "Today Western Digital is announcing their WD20WEADS drive, otherwise known as
the WD Caviar Green 2.0TB. With 32MB of onboard cache and special power management algorithms that balance spindle speed and transfer rates, the WD Caviar Green 2TB not only breaks the 2 terabyte barrier but also offers an extremely low-power
profile in its standard 3.5" SATA footprint. Early testing shows it keeps pace with similar capacity drives from Seagate and Samsung."
It's really only 1800 Gigs.
Apperently they are the same. I was a little bit surprised, too.
Seagate does not own Western Digital. You are likely thinking of Maxtor.
No, he didn't imply raid 5. (You did seem to infer that, however.)
Raid 1 would only require two drives. But having three lets you do raid 1, and then periodically remove one of the drives and store it safely offsite and then replace it with the other drive and let the raid rebuild itself. That *is* a proper backup -- though personally I'd just periodically update one backup drive with rsync or something similar with the other backup drive being kept offsite.
Every time a new, larger drive comes out, people say, "That much data in one drive is dangerous!"
So here's what you do. Go buy ten 200GB drives. RAID them together. Who do you think will lose data, you, with ten times the possible failure points, or me with only one?
Just back it up, biznatch!
Well, of course backups are the solution. And anyone with half a clue and some important data has nobody to blame but themselves if they don't have a backup.
But if you've got 10x 200 GB HDDs, and one of them fails, you've only lost 200 GB. And in a RAID setup you might not even notice that single drive failure...which means you can easily slot in a new drive and never lose any data.
While if you're running 1x 2 TB HDD, and that one drive fails, you're pretty much hosed. In this situation you'll be rebuilding your working set from a backup, which might very well take a while. It's certainly more disruptive than slotting in a new drive while your RAID keeps everything up and running with no downtime at all.
The part that concerns me is that live storage seems to be outpacing backup capacity. Sure, LTO4 can hold about 1.5 TB with decent compression... But that isn't even the full capacity of a single one of these drives. RAID a few of them together and you've completely exceeded that tape's capacity. It's getting to the point where the only solution is going to be dumping data to more HDDs, or selling robotic tape libraries to everyone.
"Work is the curse of the drinking classes." -Oscar Wilde
If the HDD does the same caching according to nearly the same principles, won't the data on the disk cache nearly always be a subset of the disk cached in RAM? Meaning: doesn't the disk cache have no effect whatsoever?
No, because the OS does not know about the physical layout of sectors on the disk and the HDD controller does. Therefore, it can reorder requests appropriately to maximise performance.
Disabling the cache on a hard disk gives a massive performance hit, especially for writes. They become nearly an order of magnitude slower.
You should look into rdiff-backup instead of rsync for your nightly backup to the offsite location. rdiff-backup keeps a set of compressed reverse-diffs in each directory that is backed up so that you can restore a file that's lost.
Well, you could click twice more, once on this (in the linked PR) http://wdc.com/en/products/Products.asp?DriveID=576 and then on the "Specifications" tab (I hate web 2.0 shit like this where you can't properly link to content).
Power Dissipation
Read/Write 7.4 Watts
Idle 4.0 Watts
Standby 0.97 Watts
Sleep 0.97 Watts
For comparison, here are the number for the 1TB (32MB cache)
Current Requirements
Power Dissipation
Read/Write 5.4 Watts
Idle 2.8 Watts
Standby 0.40 Watts
Sleep 0.40 Watts
I don't understand why Standby/Sleep power use more than doubled... As for the Active, I assume that's due to spinning 2x the platters and added processing power to be able to process the data coming off those platters 2x the speed.
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RAID 5+1 is not a backup solution either. You have created a fault tolerant scenario. Backups are there for after the rebuild when you find out that there are additional issues. The issue is not just the part where a drive can be unusable. People have already given scenarios about what can happen to the data. Any "Backup" solution should keep the data in at least 3 places, one of which, should be portable. Tapes, DVDs, removable disks, etc that can be away from the site.
What good is your RAID if you just had a power spike take out the disks along with their motherboard? Small flood in the room took out your tapes and system? Data's all gone now.
There's another problem. Take a look at this excellent article:
http://blogs.zdnet.com/storage/?p=162
SATA drives are commonly specified with an unrecoverable read error rate (URE) of 10^14. Which means that once every 100,000,000,000,000 bits, the disk will very politely tell you that, so sorry, but I really, truly can't read that sector back to you.
...
Disk drive capacities double every 18-24 months. We have 1 TB drives now, and in 2009 we'll have 2 TB drives.
With a 7 drive RAID 5 disk failure, you'll have 6 remaining 2 TB drives. As the RAID controller is busily reading through those 6 disks to reconstruct the data from the failed drive, it is almost certain it will see an URE. So the read fails. And when that happens, you are one unhappy camper. The message "we can't read this RAID volume" travels up the chain of command until an error message is presented on the screen. 12 TB of your carefully protected - you thought! - data is gone. Oh, you didn't back it up to tape? Bummer!
The government can't save you.
Simple: Buy two, and use one in an eSATA hard drive cradle/dock. Once a night, turn on the dock, back up the data, then turn it off.