RAID issues on Western Digital Hard disk

Is it true that Western Digital caviar Green hard disk are not recommended for RAID configuration

I have 640GB 16mb cache western digital hard disk with green color sticker on it. i wanted to buy one more hard disk for RAID but my dealer said there are some complaints to use raid in WD green HDD

is that true????

Thanks in advance

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Not sure if there is a specific problem the dealer was referring to, but it should at least function in a proper array. Since they do use some variable spin technology to reduce power consumption, it may cause some slow downs in the array, but I can't say for sure how they perform from experience.

Reply to wathman

There's nothing wrong whatsoever with using a green drive in a RAID array. You just have to understand why you're doing it and if it makes the best sense for you.

RAID arrays are used for two main purposes:

- improving performance by spreading the I/O load over multiple drives (much like a multi-core CPU). This is what RAID-0 does for you.

- improving reliability by creating redundant copies of the data. This is what RAID-1 does (by keeping two complete copies of the data), and also what RAID-5 does (by keeping parity information). (Both these RAID levels also give you improvements in read performance by spreading the I/O load over multiple spindles, but they hurt write performance - only slightly for RAID-1 and a lot for RAID-5).

The only reason a green drive might be an issue in a RAID array is if you're trying to use RAID to get better performance. In that case, since green drives have generally poorer performance it would make more sense to choose a higher-performing drive (such as the WD "black" series).

But if you have some green drives sitting around already, then you'll get better performance out of them by putting them into a RAID-0 set. It just won't be as good as the performance you'd get out of drives that perform better in the first place.

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Reply to sminlal

sminlal wrote :

There's nothing wrong whatsoever with using a green drive in a RAID array. You just have to understand why you're doing it and if it makes the best sense for you.

RAID arrays are used for two main purposes:

- improving performance by spreading the I/O load over multiple drives (much like a multi-core CPU). This is what RAID-0 does for you.

- improving reliability by creating redundant copies of the data. This is what RAID-1 does (by keeping two complete copies of the data), and also what RAID-5 does (by keeping parity information). (Both these RAID levels also give you improvements in read performance by spreading the I/O load over multiple spindles, but they hurt write performance - only slightly for RAID-1 and a lot for RAID-5).

The only reason a green drive might be an issue in a RAID array is if you're trying to use RAID to get better performance. In that case, since green drives have generally poorer performance it would make more sense to choose a higher-performing drive (such as the WD "black" series).

But if you have some green drives sitting around already, then you'll get better performance out of them by putting them into a RAID-0 set. It just won't be as good as the performance you'd get out of drives that perform better in the first place.

I prefer performance over data security so i should go for RAID 0 right?

My dealer is ready to exchange the HDD so shall i implement RAID on 2 HDD of western Digital caviar green 640GB or 2 HDD of Seagate 500GB

which one is better for RAID seagate or WD caviar green.

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Reply to max1989

WD's "RE" (RAID Edition) HDDs support Time-Limited Error Recovery ("TLER" ):

http://www.wdc.com/en/products/pro [...] anguage=en

As a non-TLER HDD fills up with data, the error detection firmware
might take too long, and the RAID controller may drop that HDD
from a RAID array.

MRFS

Message quoted 1 times

Reply to MRFS

max1989 wrote :

I prefer performance over data security so i should go for RAID 0 right?

That's right.

max1989 wrote :

My dealer is ready to exchange the HDD so shall i implement RAID on 2 HDD of western Digital caviar green 640GB or 2 HDD of Seagate 500GB

Well you didn't say specifically which Seagate drives you're referring to (and I don't have any particular familiarity with Seagate drives anyway), but basically you want to get a drive with the fastest access times you can find. For example, a drive with 9ms access time is better than one with 11ms access time.

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Reply to sminlal

MRFS wrote :

As a non-TLER HDD fills up with data, the error detection firmware might take too long, and the RAID controller may drop that HDD from a RAID array.MRFS

Interesting. Do you know what the timeout period would be before a typical RAID controller would drop the drive? That could be a real issue with green drives since they basically power themselves down after a few seconds of inactivity and require a few seconds to get back into "ready" status.

One would hope that the timeout period could be customized to deal with that sort of issue.

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Reply to sminlal

sminlal wrote :

Interesting. Do you know what the timeout period would be before a typical RAID controller would drop the drive? That could be a real issue with green drives since they basically power themselves down after a few seconds of inactivity and require a few seconds to get back into "ready" status.

One would hope that the timeout period could be customized to deal with that sort of issue.

Typically around 8 seconds with integrated driver/host RAID solution. Some hardware RAID cards allows you to change that value. Mine is through LSI's MegaCLI which I have set to 30s as I'm not using HDDs with TLER in a array.
Of course with any WD drives you can use a utility downloadable from their site (forgot what it's called) to enabled TLER which is defaulted to 6 seconds timeout I think.

I am pretty sure no drive spins itself down without a command given to it.

Message edited by wuzy on 08-05-2009 at 10:12:17 AM

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Reply to wuzy

On the GP drives TLER is disabled by default, on the "Raid Edition" drives, this feature is enabled by default.

In either case, if there is a bad sector on one of the RAID members; it will get kicked out of the array. TLER can't protect against that, but it can protect against a stalling/hanging system while one RAID-member disk is performing recovery.

------------------------------ ...man will occasionally stumble over the truth, but usually manages to pick himself up, walk over or around it, and carry on.
Reply to sub mesa

From the Western Digital website:

Western Digital manufactures desktop edition hard drives and RAID Edition hard drives. Each type of hard drive is designed to work specifically in either a desktop computer environment or a demanding enterprise environment.

If you install and use a desktop edition hard drive connected to a RAID controller, the drive may not work correctly unless jointly qualified by an enterprise OEM. This is caused by the normal error recovery procedure that a desktop edition hard drive uses.

When an error is found on a desktop edition hard drive, the drive will enter into a deep recovery cycle to attempt to repair the error, recover the data from the problematic area, and then reallocate a dedicated area to replace the problematic area. This process can take up to 2 minutes depending on the severity of the issue. Most RAID controllers allow a very short amount of time for a hard drive to recover from an error. If a hard drive takes too long to complete this process, the drive will be dropped from the RAID array. Most RAID controllers allow from 7 to 15 seconds for error recovery before dropping a hard drive from an array. Western Digital does not recommend installing desktop edition hard drives in an enterprise environment (on a RAID controller).

Western Digital RAID edition hard drives have a feature called TLER (Time Limited Error Recovery) which stops the hard drive from entering into a deep recovery cycle. The hard drive will only spend 7 seconds to attempt to recover. This means that the hard drive will not be dropped from a RAID array. Though TLER is designed for RAID environments, it is fully compatible and will not be detrimental when used in non-RAID environments.

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Reply to Cybertech1

Quote :

Western Digital does not recommend installing desktop edition hard drives in an enterprise environment

There they have a point, in an enterprise environment. You don't want your box being down/unresponsive for 2 minutes because one of many disks is doing recovery.

But for home users, the result is the same: after the x seconds with TLER enabled, the device will give up its recovery and report a read failure. The RAID-engine will then kick the drive out of the array. Some try again for a few times (the same sector) but they will still kick the drive out.

On Linux/BSD you can see timeouts happening, and the only issue i ran across was setting disks to spin down to conserve power in a RAID-config would lead to timeouts and disks being kicked out. After setting the timeout value to 60 seconds, this issue disappeared. FreeBSD 8 is also known to automatically increase the timeout of the device when its spun down.

So if you're using Linux or BSD, even a 2 minute recovery time wouldn't be disastrous if you configured it right. It could cause the server to hang when any disk is doing recovery, but for home users getting it to work is more important than 2 minutes downtime. Where enterprise environments use redundancy and would want to swap out any disk as soon as possible whenever the smallest suspicion of malfunction arises.

So, TLER is not a "must-have" in home RAID environments, and may even make otherwise recoverable data irrecoverable, unless you use redundancy like RAID1/3/4/5/6. Either way, having an operating system that allows you to set the timeout to a high value would be more valuable than having TLER, for home users.

------------------------------ ...man will occasionally stumble over the truth, but usually manages to pick himself up, walk over or around it, and carry on.
Reply to sub mesa

Cybertech1 wrote :

From the Western Digital website:

Western Digital manufactures desktop edition hard drives and RAID Edition hard drives. Each type of hard drive is designed to work specifically in either a desktop computer environment or a demanding enterprise environment.

If you install and use a desktop edition hard drive connected to a RAID controller, the drive may not work correctly unless jointly qualified by an enterprise OEM. This is caused by the normal error recovery procedure that a desktop edition hard drive uses.

ok if western digital has this issue what about seagate 500GB sata 16mb cache (Model No. : ST3500418AS)

Reply to max1989

sminlal wrote :

That's right.
Well you didn't say specifically which Seagate drives you're referring to (and I don't have any particular familiarity with Seagate drives anyway), but basically you want to get a drive with the fastest access times you can find. For example, a drive with 9ms access time is better than one with 11ms access time.

i am confused with western digital caviar green 640 GB 16mb cache and seagate 500GB (Model No. : ST3500418AS). so which one u prefer for raid 0.

Reply to max1989

Pick the WD Green drives if you'll be storing large files like when downloading stuff from the internet. Even a music file of 3MB is considered large. Windows has many files of less than 4 kilobytes, which demands different performance characteristics.

So the Green drives are excellent for large files (sequential transfers), they may be less suitable to load your operating system, applications and games on. It won't run terribly slow, but it won't be as fast as other modern non-Green drives.

The green drives do keep very cool since they use little power and are also very quiet, so i would recommend them.

------------------------------ ...man will occasionally stumble over the truth, but usually manages to pick himself up, walk over or around it, and carry on.
Reply to sub mesa

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