RAID question

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johns

Last time I used a RAID setup was in my early
Novell days. I think the server was a 386, and I
was ( theoretically ) using the RAID config as
a backup to the OS in case of hard drive failure.
Naturally, the hard drive failed in such a way
that it corrupted the mirror drive, and then I
had 2 bad drives. A few years ago, when I started
seeing RAID as a part of the mobo capabilities,
I tried it again, and all I ever figured out about
that is you can' t mix IDE boot drives with SATA
RAID drives. WinXP could not sort it out, and
I generated a flakey bootup condition, that
constantly reported boot drive failure. After that,
I switched to SATA boot drives with RAID disabled.
These days, the know-it-alls keep telling me
that I should be running RAID-0 for data security
????????????????? I though RAID-0 was
for faster data access by using a virtual partition
spread across several hard drives, and had
nothing to do with mirroring or security ... just
speed in sequential data base access. I've been
on the net reading the RAID jargon, and that
sure has not improved over the years. One of
the RAIDS can use mirroring, but, in my opinion,
that is not for security. That is for reducing
downtime if you can hot-swap a failing drive
while the system is still running. Who gives
a damn about hot-swapping a stand-alone
PC, so someone can sit there and keep
typing while I swap in a new hard drive ???
If the PC has a shared data base, why is
that data base not copied off to an external
USB drive for security? Why mirror it? My
experience with mirrors is bad writes get
"mirrored" too. You can sit there like a total
dumbass and corrupt the share for weeks,
and you have nothing. Anybody out there
understand RAID on a stand-alone PC ?

johns
 
RAID0 is striping, meaning that you get the combined size of both hard
drives, and Windows will see them as one large drive. The advantage of
RAID0 is speed. Since all written data is split evenly across the
raided disks, your read/writes will tend to be faster. People that do
this on PCs usually do it for gaming, as it increases the loadtime of
games. Now obviously, if you have critical data, you don't want RAID0,
because if one disk fails, so does the other, theres no hope of
recovering what was on those disks.

RAID1 is mirroring, meaning that both disks are exactly the same. This
tends to slow down the PC because all writes need to be performed
twice. When using RAID1, you'll only have as much space as 1 of your
disks. I can't think of anyone that would use RAID1 on a PC, it's just
not that useful.

RAID5 is striping with fault tolerance. In this arrangement, you need a
minimum of three disks. However, you'll only have the space of 2 of
those 3 disks to use. Should any disk fail, you can pop in a new disk
and the two functioning disks will be able to recreate the lost data.
This offers a combination of both RAID0 and RAID1, although I've never
seen anyone use it on a PC, mostly just servers.

Hopefully this helps.

--Bill
 
I've read the definitions, but it is what is behind those
definitions nobody ever talks about. For example, in
RAID1 what is there that stops mirroring of bad writes
in the case where corrupt files are copied on to the
PC, and then mirrored to the backup. And that is a
biggie. I see it all the time with corrupt CAD files
where the "project" was never properly defined, or
no template was used to define the layers and extents
of the drawings. I've also seen it archive all kinds
of viruses that immediately go active during recovery.
Problem with this technology is the "mythology"
that has grown up around it ... claiming it to be
some kind of secure low-maintainance backup
in an Engineering workstation environment, where
the Engineers simply don't want to hit a lick in
that regard. I always viewed RAID as technology
that kept servers operational during repairs, and
had no place in the single PC environment. Reason
I'm asking all this is I've got jargon users wanting
me to implement IT .. when I already have disk
imaging, and copy off to network drives and USB
drives that power down and archive the updates.
I tend to babysit those things manually, checking
reliability of the archived data, and never overwriting
it for several years .. if ever. I don't think these people
know what they are talking about, and the problem
is the jargon on the internet is incomprehensible
and wishy-washy ... using words like "might be
able" .. heh! As for game speed ... my game box
kicks ass. The secret there is not striped hard
drives. It is 2 gigs of ram and an nVidia GF7900GTO
running in an AMD Athlon 64 3700+ box. That has
got to be many times faster than a striped drive
config ever thought about being.

johns
 
johns said:
I've read the definitions, but it is what is behind
those definitions nobody ever talks about.
Click to expand...

Those are part of the basics.
For example, in RAID1 what is there that stops mirroring
of bad writes in the case where corrupt files are copied
on to the PC, and then mirrored to the backup.
Click to expand...

Nothing, you get the corrupted file on both drives.
And that is a biggie.
Click to expand...

Its irrelevant to RAID.
I see it all the time with corrupt CAD files where the
"project" was never properly defined, or no template was
used to define the layers and extents of the drawings.
Click to expand...

Nothing any RAID can do about something like that.
I've also seen it archive all kinds of viruses
that immediately go active during recovery.
Click to expand...

Yes, nothing any RAID can ever do about those either.

Thats what proper backups are for, so you can
restore to the state before the virus showed up.
Problem with this technology is the "mythology"
that has grown up around it ... claiming it to be
some kind of secure low-maintainance backup
in an Engineering workstation environment,
Click to expand...

No one who knows anything about RAID is ever stupid
enough to claim that, and plenty keep pointing out that
RAID is no substitute for real backups.

The main advantage of RAID in the redundancy area
is that it minimises the downtime when a hard drive
fails, and allows the system to be used while the
failed drive is replaced etc and minimises the need to
actually restore from backup with the time that takes.
where the Engineers simply don't want to hit a lick in that regard.
Click to expand...

Not clear what you mean there.
I always viewed RAID as technology that
kept servers operational during repairs,
Click to expand...

And to allow the repairs to be done when convenient.
and had no place in the single PC environment.
Click to expand...

Thats not true if you need high uptimes,
like say with share trading etc.

Or even if you just want high productivity out of the PC
and want to be able to continue to do what the PC is there
for and to do the repairs when its more convenient rather
than when the failure has produced an unusable system.

Corse you can also make a case for even better
redundancy, more than one PC so you can carry
on regardless of whatever has failed too.
Reason I'm asking all this is I've got jargon users
wanting me to implement IT .. when I already have
disk imaging, and copy off to network drives and USB
drives that power down and archive the updates.
Click to expand...
I tend to babysit those things manually, checking
reliability of the archived data, and never overwriting
it for several years .. if ever. I don't think these people
know what they are talking about, and the problem
is the jargon on the internet is incomprehensible and
wishy-washy ... using words like "might be able" .. heh!
Click to expand...

Sure, plenty can never grasp the basics.
As for game speed ... my game box kicks ass.
The secret there is not striped hard drives. It is
2 gigs of ram and an nVidia GF7900GTO
running in an AMD Athlon 64 3700+ box. That
has got to be many times faster than a striped
drive config ever thought about being.
Click to expand...

Depends on how much the drive is used. There are some
situations where striped drives does improve performance.
 
Rod said:
Those are part of the basics.


Nothing, you get the corrupted file on both drives.


Its irrelevant to RAID.


Nothing any RAID can do about something like that.


Yes, nothing any RAID can ever do about those either.

Thats what proper backups are for, so you can
restore to the state before the virus showed up.


No one who knows anything about RAID is ever stupid
enough to claim that, and plenty keep pointing out that
RAID is no substitute for real backups.

The main advantage of RAID in the redundancy area
is that it minimises the downtime when a hard drive
fails, and allows the system to be used while the
failed drive is replaced etc and minimises the need to
actually restore from backup with the time that takes.


Not clear what you mean there.


And to allow the repairs to be done when convenient.


Thats not true if you need high uptimes,
like say with share trading etc.

Or even if you just want high productivity out of the PC
and want to be able to continue to do what the PC is there
for and to do the repairs when its more convenient rather
than when the failure has produced an unusable system.

Corse you can also make a case for even better
redundancy, more than one PC so you can carry
on regardless of whatever has failed too.



Sure, plenty can never grasp the basics.


Depends on how much the drive is used. There are some
situations where striped drives does improve performance.
Click to expand...

Thank you all for this discussion. I was caught in the Raid jargon and
hype and had almost decided to go the extra and include it on the new
home dream computer, but seeing what you have written I can see that it
isn't something I would use. Possibly Raid0 for gaming, but I can see
advantages to doing backup through other means, external drives we use
to pass data from pc to pc etc.
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johns je napisal:
These days, the know-it-alls keep telling me
that I should be running RAID-0 for data security
?????????????????
Click to expand...

That only makes sense if you think of it like... a disk that is part of
a RAID 0 array cannot be accessed without being in another RAID 0 array
with the other disk. E.g. if somebody steals just one of your disks
they cannot access the contens.

But that's nonsense IMHO.
Anybody out there understand RAID on a stand-alone PC ?
Click to expand...

I have a RAID0 array in my PC... tho the true concept of Personal
Computer is foregin to me as I only have servers and my office and home
desktops all have servers on them too (= 24/7 operation).

I hated the physical bottleneck on the speed of the disk drives (and
the sounds they make while working), so that's why I got myself a RAID0
which fixed it all. A RAID card also provides extra cache and has a
standalone controller which does not use the CPU for what it does, so I
get a little extra kick here and there from that. Naturally I got
myself some good harddrives and I don't trust SATA (where I work we
once had to replace 6 SATA disks after a storm for badsectors, ATA
disks were untouched), so my excuse really does not explain very well
why most new computers have built-in SATA RAID controller.

SATA RAID seems to be really cheap to implement and is the next logical
step in added harddrive performance, that's my oppinion why motherboard
manufacturers slap "on-board RAID" labels on some of their products.
 
johns je napisal:
As for game speed ... my game box
kicks ass. The secret there is not striped hard
drives. It is 2 gigs of ram and an nVidia GF7900GTO
running in an AMD Athlon 64 3700+ box. That has
got to be many times faster than a striped drive
config ever thought about being.
Click to expand...

That's old for today's standards, BTW and using RAID0 to improve
performance is a very good thing to do. Use chunks that represent half
the size of the majority of your files (1 KB in most home use cases).
You won't notice a performance boost on Linux due to the way file
access is implemented there, but on a Windows computer the difference
is huge.

It can be benchmarked by transfering big files from one RAID0 array to
another, or by transfering big files from a RAID0 array over a LAN. I
tried, copied Office CD onto the harddisk and installed it over a
Windows share... setup copied all the required files in four seconds.
Try if your gaming box can do that.
 
Windows share... setup copied all the required files in four seconds.
Try if your gaming box can do that.
Click to expand...

It sure can. I have a gigabit lan, and you were only moving
about 200 meg. Still, why? 99% of my access is random.
I'm not moving big anything on a PC. I'm far more concerned
with security than speed. In games, the road to speed and
smooth operation is ram. The biggest level in Far Cry is
about 600 meg, and then a bunch of stacks that will
collide if you don't have 2 gigs to play in. If I was pulling
anything from a hard drive, it would produce screen
stuttering in the game. My 7900 is a 24 pipe card with
256 meg ram. That is real speed.

johns
 
SATA RAID seems to be really cheap to implement and is the next logical
step in added harddrive performance, that's my oppinion why motherboard
manufacturers slap "on-board RAID" labels on some of their products.
Click to expand...

Maybe they are thinking about PVRs, and the huge data
storage and retrieval problems associated with that ..
esp if we ever get digital cable TV on fiber .. like we
were suppose to. I read somewhere about tax dollars
going to building that infrastructure, but so far I don't
think it has happened ??? A RAIDed multimedia
system of that quality could benefit from the faster
access of huge video files ??

johns
 
Maybe they are thinking about PVRs, and the huge data
storage and retrieval problems associated with that ..
Click to expand...

Unlikely, I can do 4 channels on a rather older 900MHz
Celeron fine and be playing back one channel fine too,
with a completely bog standard modern hard drive.
esp if we ever get digital cable TV on fiber .. like we
were suppose to. I read somewhere about tax dollars
going to building that infrastructure, but so far I don't
think it has happened ??? A RAIDed multimedia
system of that quality could benefit from the faster
access of huge video files ??
Click to expand...

Not necessary for those.
 
Thanks guys, you just bailed me from the
know-it-alls. I dropped a printout on their
desks :-)

johns
 
johns je napisal:
It sure can. I have a gigabit lan, and you were only moving
about 200 meg. Still, why? 99% of my access is random.
I'm not moving big anything on a PC.
Click to expand...

RAID0 with small blocks outpreforms your harddrive alone on random and
sequential access.
 
WJRutledge said:
RAID0 is striping, meaning that you get the combined size of both hard
drives, and Windows will see them as one large drive. The advantage of
RAID0 is speed. Since all written data is split evenly across the
raided disks, your read/writes will tend to be faster. People that do
this on PCs usually do it for gaming, as it increases the loadtime of
games. Now obviously, if you have critical data, you don't want RAID0,
because if one disk fails, so does the other, theres no hope of
recovering what was on those disks.

RAID1 is mirroring, meaning that both disks are exactly the same. This
tends to slow down the PC because all writes need to be performed
twice. When using RAID1, you'll only have as much space as 1 of your
disks. I can't think of anyone that would use RAID1 on a PC, it's just
not that useful.

RAID5 is striping with fault tolerance. In this arrangement, you need a
minimum of three disks. However, you'll only have the space of 2 of
those 3 disks to use. Should any disk fail, you can pop in a new disk
and the two functioning disks will be able to recreate the lost data.
This offers a combination of both RAID0 and RAID1, although I've never
seen anyone use it on a PC, mostly just servers.

Hopefully this helps.

--Bill
Click to expand...

I disagree with the RAID1 not being useful at home. I use my system
for everything at home and really don't want to be forced to have to
rebuild it, then restore from backups on a weekday night or weekend
day. Disks and RAID controllers being relatively cheap these days it
is a small investment to have a mirror configuration. I don't do any
gaming or high end video stuff, so the performance hit is minimal for
me. I also do weekly full backups, and use Memeo for critical data
files. This backs them up as they are changed.

-Jim
 
DustWolf said:
johns je napisal:
Click to expand...
RAID0 with small blocks outpreforms your harddrive alone on random and
sequential access.
Click to expand...

BUT ONLY ON BENCHMARK TESTS!!! In the real-world you SHOULD use the
default strip size, which is typically 128K. Drop down to a smaller strip
size ONLY if you are REALLY sure. 64K or 32K are workable and perhaps
prudent in your stated case, but going lower than that will most likely
RAISE cpu overhead at the expense of performance.

BTW, trying to force the cluster size to match the strip size is also
an old-wives-tale; don't waste your time trying to do this, it buys you
nothing at all, and you give up features of NTFS by doing so.
 
Unless the mirror itself corrupts. And then, your data is
gone. So you still ( are doing backups ). In my case, I
do images which are very fast, and then I archive them
against corruption of any kind. Image creation is also
unattended .. both create and restore ... so the actual
time you spend is about 30 seconds going each way.
Best of all, a power down archive is 100% secure
even if you had to replace the entire computer. I don't
find it annoying to also do manual copies of important
docs to the backup drive. That way, I'm sure it is
working. RAID must have some better use than
just totally minimizing backups on a single PC. It is
just safer to monitor that in person.

johns
 
johns said:
Unless the mirror itself corrupts. And then, your data is
gone. So you still ( are doing backups ). In my case, I
do images which are very fast, and then I archive them
against corruption of any kind. Image creation is also
unattended .. both create and restore ... so the actual
time you spend is about 30 seconds going each way.
Best of all, a power down archive is 100% secure
even if you had to replace the entire computer. I don't
find it annoying to also do manual copies of important
docs to the backup drive. That way, I'm sure it is
working. RAID must have some better use than
just totally minimizing backups on a single PC. It is
just safer to monitor that in person.

johns
Click to expand...

I'm not sure if this is in reply to my post, but here are my thoughts
on that. I don't see how you can do an image of even a 20 gig drive in
30 seconds, including shut down, image, an boot up. But even so, you
still need another drive. So now all you have is the cost of a RAID
controller and a one time setup of the mirror to contend with. Beyond
that there is no user intervention. The performance hit is minimal,
especially when compared with the image process.

But I may be wrong about your times. I have always used Ghost for
imaging. How do you do it, in 30 seconds? How big a drive are we
talking about.

Thanks,
Jim
 
Rod Speed said:
Those are part of the basics.


Nothing, you get the corrupted file on both drives.


Its irrelevant to RAID.


Nothing any RAID can do about something like that.


Yes, nothing any RAID can ever do about those either.

Thats what proper backups are for, so you can
restore to the state before the virus showed up.


No one who knows anything about RAID is ever stupid
enough to claim that, and plenty keep pointing out that
RAID is no substitute for real backups.

The main advantage of RAID in the redundancy area
is that it minimises the downtime when a hard drive
fails, and allows the system to be used while the
failed drive is replaced etc and minimises the need to
actually restore from backup with the time that takes.


Not clear what you mean there.


And to allow the repairs to be done when convenient.


Thats not true if you need high uptimes,
like say with share trading etc.

Or even if you just want high productivity out of the PC
and want to be able to continue to do what the PC is there
for and to do the repairs when its more convenient rather
than when the failure has produced an unusable system.

Corse you can also make a case for even better
redundancy, more than one PC so you can carry
on regardless of whatever has failed too.



Sure, plenty can never grasp the basics.


Depends on how much the drive is used. There are some
situations where striped drives does improve performance.
Click to expand...
well done
 
jtpryan said:
I'm not sure if this is in reply to my post, but here are my thoughts
on that. I don't see how you can do an image of even a 20 gig drive in
30 seconds, including shut down, image, an boot up. But even so, you
still need another drive. So now all you have is the cost of a RAID
controller and a one time setup of the mirror to contend with. Beyond
that there is no user intervention. The performance hit is minimal,
especially when compared with the image process.

But I may be wrong about your times. I have always used Ghost for
imaging. How do you do it, in 30 seconds? How big a drive are we
talking about.

Thanks,
Jim
Click to expand...

agree with every point you make for RAID 1.
I'm fighting some of the tech setup issues right now. but:

the controller on the mb
mirror drive cost $100. (300 gigs is good for most non video
squirrels)
happening in real time

no other costs!! no other software to buy. not a nanoseconds time
spent worrying, monitoring, spending cycles worring about the dreaded.
how can you not love a near bulletproof hardware insurance on the poor
disks biggest problem, the crash.

Corruption Recovery should be another thread.
 
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