is RAID really useful??

  • Thread starter Thread starter esara
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esara

Hi I am reading about RAID and I have found some MotherBoard are
supporting it (but you have to pay more) But now I wonder why do we
need Raid?? is it really used and useful featrue?? why I am saying
this is becuase

1) Raid 1 is mirroring right? but if a file is corrupted then it will
be stored in both drivers as a corrupted file.. But Raid is useful if
one harddrive mechanically die then i can use the other.. but this is
not going to happen that frequently!!

2) Raid 0 is striping.. well if there are 2 files, for example
file1.txt (in HD1) and file2.txt (in HD2) and lets say my email
software need to read file1.txt and my MSWords wants to read file2.txt
then these 2 software will be able to access these 2 files at the same
time. If not for Raid and we have only 1 HD then, first the OS will
try to access file1.txt and give it to email software and then the OS
will try to access file2.txt and try to give it to MSwords and this
will take longger time, I am right??

Thanks
 
esara said:
1) Raid 1 is mirroring right? but if a file is corrupted then it will
be stored in both drivers as a corrupted file.. But Raid is useful if
one harddrive mechanically die then i can use the other.. but this is
not going to happen that frequently!!
Click to expand...

RAID 1 is a seamless way to have a backup HD. Not only do you not have to
backup your data as frequently (if you need/want an off-site backup), but you
have a full HD available, ready to go, if the other dies.

If you don't need/want that type of protection, don't bother.

2) Raid 0 is striping.. well if there are 2 files, for example
file1.txt (in HD1) and file2.txt (in HD2) and lets say my email
software need to read file1.txt and my MSWords wants to read file2.txt
then these 2 software will be able to access these 2 files at the same
time. If not for Raid and we have only 1 HD then, first the OS will
try to access file1.txt and give it to email software and then the OS
will try to access file2.txt and try to give it to MSwords and this
will take longger time, I am right??
Click to expand...

Nope.

In RAID 0, the 2 HDs look like a single HD to the software. The RAID controller
allows the software to write parts of the file to both HDs simultaneously, so
each HD head is doing part of the work. You may not notice a difference with
small files, but will notice it when working with large files such as videos or
large graphics.
 
esara said:
1) Raid 1 is mirroring right? but if a file is corrupted then it will
be stored in both drivers as a corrupted file..
Click to expand...

Correct. RAID 1 is *NOT* a backup strategy.

But Raid is useful if
one harddrive mechanically die then i can use the other.. but this is
not going to happen that frequently!!
Click to expand...

Aren't we optimistic? :)

2) Raid 0 is striping.. well if there are 2 files, for example
file1.txt (in HD1) and file2.txt (in HD2) and lets say my email
software need to read file1.txt and my MSWords wants to read file2.txt
then these 2 software will be able to access these 2 files at the same
time. If not for Raid and we have only 1 HD then, first the OS will
try to access file1.txt and give it to email software and then the OS
will try to access file2.txt and try to give it to MSwords and this
will take longger time, I am right??
Click to expand...

RAID does not operate on the file level. It's completely transparent to
the operating system. With RAID 0, any file will have its data equally
distributed on the drives in the array. When you read or write the
file, it occurs simultaneously across all drives.


-WD
 
Hi I am reading about RAID and I have found some MotherBoard are
supporting it (but you have to pay more) But now I wonder why do we
need Raid?? is it really used and useful featrue?? why I am saying
this is becuase

1) Raid 1 is mirroring right? but if a file is corrupted then it will
be stored in both drivers as a corrupted file.. But Raid is useful if
one harddrive mechanically die then i can use the other.. but this is
not going to happen that frequently!!
Click to expand...

The key to deciding whether to RAID1 or not is what is
your time worth if the system goes down due to a failed
drive. For servers, the redundancy is worth it when you
can just drop a new drive in and let it auto-rebuild
without downtime. For home systems... eh, maybe not
worth it.

A better choice for home might be single disk, with
Norton Ghost or Symantec Drive Image (create a new image
weekly) written to a 2nd drive. Also, use the 2nd drive
as a backup device (mirror just your data files from the
primary to the secondary daily using something like
Second Copy 2000). As long as you're diligent about
creating and updating the images (Drive Image might be
better software in this regard), you get the advantages
of RAID1 (immunity to a failed drive) but with the bonus
that you can restore your system back to a known working
point should a software install go bad. (Make sure you
backup user data seperately so you can re-load the
image, then restore your user data.)

RAID1/RAID5 is not a backup strategy (like Will said).
It's more of a disaster prevention strategy. If the O/S
corrupts a file, it will end up being corrupt on both
disks. (Or if the file system corrupts itself, it will
end up corrupt on both drives.)
 
John R Weiss wrote
RAID 1 is a seamless way to have a backup HD. Not only do you not have to
backup your data as frequently (if you need/want an off-site backup), but you
have a full HD available, ready to go, if the other dies.

In RAID 0, the 2 HDs look like a single HD to the software
Click to expand...

could you also explain what is "striping" ? several new dell precision
systems come preconfigured with Serial ATA and striping enabled on 2
drives
 
RAID 0 is also called "striping," which, in its most simple sense, uses a
pair of hard drives to become one larger hard drive onto which every other
cluster of information is written simultaneously to each physical drive.
What this means is that your hard drive write speed performance almost
doubles, since the information is being doubled up and split up to be
written at the same time to two separate drives.

What this can also mean is that without additional forms of backup
protection, if just one of the hard drives fail (all hard drives are really
just mechanical parts) then the information on the remaining healthy hard
drive is practically useless, since it only contains every other cluster
(not file) of the original data...very scary if you don't perform regular
backups. The failure of just one drive will result in all data in an array
being lost and RAID 0 should never be used in mission critical environments.

Please note that if you use drive imaging programs such as Norton Ghost® or
PowerQuest DriveImage®, that drives in a RAID array may not be successfully
restored from a created image. Hardware (controller BIOS-created) arrays
might be successfully backed up and restored, but software (OS
software-managed) arrays will likely fail to be successfully backed up or
restored. The most recent versions of Norton Ghost® claims no compatibility
with RAID arrays, and the most recent version of PowerQuest DriveImage®
claims compatibility with hardware-based arrays only.

Pros: can be useful for performance gains, fairly cost-effective for most
home users (compared to RAID 1, or "mirroring"), due to only 2 identical (or
similar, but the RAID array will see the larger drive having the same
capacity of the smaller of the 2 drives, if different sizes) drives needed,
and the entire storage capacity of both drives combined can be "used"

Cons: performance gains at the expense of data security, drive imaging
programs may not work properly.

Russell
http://tastycomputers.com
 
Russell said:
Pros: can be useful for performance gains, fairly cost-effective for most
home users (compared to RAID 1, or "mirroring"), due to only 2 identical (or
similar, but the RAID array will see the larger drive having the same
capacity of the smaller of the 2 drives, if different sizes) drives needed,
and the entire storage capacity of both drives combined can be "used"

Cons: performance gains at the expense of data security, drive imaging
programs may not work properly.
Click to expand...

I disagree with your first Con, at least in practical terms.

I suppose that there is a miniscule added probability of a single drive failure
when you have 2 drives instead of 1. However, it doesn't matter if you have a
single drive or a RAID 0 array -- any single failure will obliterate your data.
A backup regimen is required in either case.
 
I was referring to someone who had 2 drives and was weighing the pros and
cons of leaving them non-RAID or creating a RAID array.. In a BASE
(non-RAID array), there is more data security with 2 drives than with 2
drives in a RAID 0 array. If you have striping across the 2 drives, one
error on one cluster of data will result in a corruption on both drives, but
in the BASE configuration, that particular scenario doesn't come into play.
All things considered, both configurations have the same amount of storage
space, but one is less prone to corruption, while the other one improves
performance. Also, I think that RAID 1 (mirroring) arrays are a waste of
resources for the average home user, halving their storage capacity at
double the price, but they are useful for mission-critical server setups.
In all configurations, however, a good backup routine is always the best way
to go.

Russell
http://tastycomputers.com
 
John said:
I disagree with your first Con, at least in practical terms.
Click to expand...

RAID 1 is generally quicker on reads, and slower on writes.

If the budget allows, "duplexing" the drives (1 controller for each
drive) is often a lot quicker.


Odie
 
| <snip>
| I suppose that there is a miniscule added probability of a single
| drive failure when you have 2 drives instead of 1. However, it
| doesn't matter if you have a single drive or a RAID 0 array -- any
| single failure will obliterate your data. A backup regimen is
| required in either case.

'regimen' ? ? ? - sounds like a merry band of people who go around editing
registries ! :-)
 
|performance. Also, I think that RAID 1 (mirroring) arrays are a waste of
|resources for the average home user, halving their storage capacity at
|double the price,

Actually, halving their storage at the same price.

Phil
 
(e-mail address removed) wrote:
|
|| performance. Also, I think that RAID 1 (mirroring) arrays are a
|| waste of resources for the average home user, halving their storage
|| capacity at double the price,
|
| Actually, halving their storage at the same price.

Or even giving the same storage capacity at double the price. ;-)
Kevin.
 
Kevin said:
(e-mail address removed) wrote:
|
|| performance. Also, I think that RAID 1 (mirroring) arrays are a
|| waste of resources for the average home user, halving their storage
|| capacity at double the price,
|
| Actually, halving their storage at the same price.

Or even giving the same storage capacity at double the price. ;-)
Kevin.
Click to expand...
or giving one over the square root of two times the capacity at the
square root of two times the cost.

dick
-- or something like that.
 
Russell said:
I was referring to someone who had 2 drives and was weighing the pros and
cons of leaving them non-RAID or creating a RAID array.. In a BASE
(non-RAID array), there is more data security with 2 drives than with 2
drives in a RAID 0 array. If you have striping across the 2 drives, one
error on one cluster of data will result in a corruption on both drives, but
in the BASE configuration, that particular scenario doesn't come into play.
Click to expand...

At a technical level, I agree with you, but at the user level I don't believe it
makes that much difference.

Assume the nonrecoverable error rate on any HD is 10**-15 (actual specs from WD
Raptor and Seagate Cheetah). The error rate on 2 HDs in an array will then be 2
x 10**-15. In a non-striped array, the "first error" could be on either drive,
and may or may not corrupt a given file. However, given the fact that virtually
ANY critical error will involve data being written to the HD, the likelihood
that the "first error" will affect a data file is extremely high. Relatively
speaking, the increased probability of data loss due to striping is quite low.

Also, if the choice of a RAID array drives the user to select a higher-quality
HD in the first place, the probability of error may actually be reduced (e.g.,
from 10**-14 for the Seagate Barracuda to 10**-15 for the Seagate Cheetah -- a
10x improvement in basic reliability). IMO, a user savvy enough to consider the
RAID 0 option will be more likely to consider the hardware options as well.

I also realize that the last paragraph does not directly apply once the user has
the HDs in hand and is ready to set up the BIOS for RAID or non-RAID. It's just
more food for thought...
 
Kevin Lawton said:
| A backup regimen is
| required in either case.

'regimen' ? ? ? - sounds like a merry band of people who go around editing
registries ! :-)
Click to expand...

Or the "Reggie" (an old comic strip) fan club...
 
John said:
At a technical level, I agree with you, but at the user level I don't believe it
makes that much difference.

Assume the nonrecoverable error rate on any HD is 10**-15 (actual specs from WD
Raptor and Seagate Cheetah). The error rate on 2 HDs in an array will then be 2
x 10**-15.
Click to expand...

This is not actually so - an actuary would make more sense of it.

To prove it wrong, assume 1 million of these drives have been sold.

Applying your calculation, there is still an ****extremely**** slim
chance of non-recoverable errors in, say, a period of a few months.

I can guarantee that within that period, a number of the original 1
million drives will have failed.

For every number of drives doubled, there is a larger chance than merely
double the previous number of drives.

Odie
 
Toshi1873 said:
The key to deciding whether to RAID1 or not is what is
your time worth if the system goes down due to a failed
drive. For servers, the redundancy is worth it when you
can just drop a new drive in and let it auto-rebuild
without downtime. For home systems... eh, maybe not
worth it.

A better choice for home might be single disk, with
Norton Ghost or Symantec Drive Image (create a new image
weekly) written to a 2nd drive. Also, use the 2nd drive
as a backup device (mirror just your data files from the
primary to the secondary daily using something like
Second Copy 2000). As long as you're diligent about
creating and updating the images (Drive Image might be
better software in this regard), you get the advantages
of RAID1 (immunity to a failed drive) but with the bonus
that you can restore your system back to a known working
point should a software install go bad. (Make sure you
backup user data seperately so you can re-load the
image, then restore your user data.)

RAID1/RAID5 is not a backup strategy (like Will said).
It's more of a disaster prevention strategy. If the O/S
corrupts a file, it will end up being corrupt on both
disks. (Or if the file system corrupts itself, it will
end up corrupt on both drives.)
Click to expand...

I chose a RAID board to have the option, even though I don't plan to use it
soon. I'm using the PATA connection just like a typical primary IDE setup.
No RAID arrays, and I do "normal" backups. But I also thought that having a
3rd PATA controller and a 4th SATA controller on board would perform better
than a PCI add on card. Was I correct?
 
Odie said:
This is not actually so - an actuary would make more sense of it.

To prove it wrong, assume 1 million of these drives have been sold.

Applying your calculation, there is still an ****extremely**** slim
chance of non-recoverable errors in, say, a period of a few months.

I can guarantee that within that period, a number of the original 1
million drives will have failed.

For every number of drives doubled, there is a larger chance than merely
double the previous number of drives.
Click to expand...


The spec is based on "bits written," not number of installed drives. With RAID
1, the number of bits written will double, so statistically the "first error"
will come twice as fast. With RAID 0, the number of bits written does not
double, so based on the actual spec the "first error" will not come any earlier.
However, since both drives are constantly operating, I chose to use the
conservative case.

Again, this is technical and statistical in nature, and a single user will not
likely be affected at all in realistic terms. However, since there is always
that chance the statistics may point at you, a backup is always a good idea.
 
OTOH, assume a home user can buy a RAID 1 array already configured, so he
doesn't have to worry about setup. He then doesn't have to worry about Norton
Ghost or similar -- the image is automatically created. If he has a HD failure,
he simply replaces the HD instead of trying to recover the image with Ghost.

An off-site backup is still a good idea, but for a non-geek who may not backup
anything at all, RAID 1 has a place. Besides, a second HD won't cost much more
these days than the software. After that, any failure will require a new HD in
any scenario, so the elegance of the recovery becomes the issue.

I chose a RAID board to have the option, even though I don't plan to use it
soon. I'm using the PATA connection just like a typical primary IDE setup.
No RAID arrays, and I do "normal" backups. But I also thought that having a
3rd PATA controller and a 4th SATA controller on board would perform better
than a PCI add on card. Was I correct?
Click to expand...

All depends on the individual implementations... One could be led to believe
that current on-board PATA/SATA HD controllers would perform better than add-on
boards. OTOH, that is not true these days with graphics adapters -- the state
of the art is such that add-on cards are much more capable than virtually any
on-board graphics...
 
Also assume that a particular home user may have installed/uninstalled a
particular program incorrectly, or that some badly-written code in some
shareware has wreaked havoc with the registry, or that a viral infection has
gummed things up...a RAID 1 array will not be useful in these instances, as
what is written to one disc is simultaneously written to the second disc,
with the problems identical on each disc. In this case, the only thing that
would restore the home user's drive(s) to a usable state would be a cloned
image or a reinstallation with needed data restored from a separate medium.
RAID 1 is only useful in the event that a physical error is present on one
of the discs. A regular backup regimen is the only way to go.

Russell
http://tastycomputers.com
 
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