Kaj za vraga je to RAID?

A lahko kdo tako lepo po domače razloži kaj je to RAID, in kaj uporabnik s tem pridobi?

Dva diska skup povežeš tko da OS vid sam enga. In pol ena fora (RAID-0) je da k se en fajl piše al pa bere z diska se pol fajla na en disk pol pa na drug disk piše. In ker se to dela na dveh diskih naenkat je pol to še enkat hitrej. Druga fora (RAID-1) je pa da k na en disk pišeš se na druzga isto napiše. In če pol en od diskov crkne OS še kr lohk prebere podatke z druzga diska. S tem se pa poveča varnost.

To pomeni, da maš pol lahko pri RAID 1 en disk uporabljen kao za backup podatkov?

Sam sicer ne uporabljam, se mi zdi to bolj serverska fora. Ampak eni pravijo, da brez RAIDa jim živeti ni (sploh v povezavi s skazi diski). Doma je bolj razširjeno zaradi hitrosti, ne verjamem, da zaradi previdnosti.

Kupis si dva ibm diska, pa das v raid 0, pol pa ti en crkne. Kaj pa potem naredit? sicer se ti vedno ostane polovica podatkov:)

ROK:ne vem, ce je mozno dva razlicna diska povezat v raid. Ali pac? al si bos mogoce dva 10gb kupo?

Evo ti nekaj malega o RAIDu:


RAID: That it is; What it does. -------------------------------
RAID is something all of us have heard about but very few of us understand,
at least fully. So lets get off on the right foot. RAID stands for Redundant
Array of Inexpensive (or Indepenadant) Disks. There are a dozen or so
theories as to why RAID was conseptualized, but the most accepted reason is
that once upon a time, not long ago, disks were small and expensive. In
order to provide a large amount of data you had to have a bunch of disks all
mounted in a single file tree, which was a real mess. So, to solve this
problem RAID was born. With RAID you could take a bunch of disks at create a
big virtual disk out of them which made administration much easier and more
logical. Over time RAID grew to include new solutions for old problems, like
disk performance, redundancy, and scalibility. And for any sceptics out
there, tell me where I can get a 10 terabyte disk drive.... that should make
us all agree that RAID has a place in the universe. Just to try and clear
things up a bit more, lets see why we don't simple just need RAID, but
actually WANT it. Let's say we're building a production NFS server that will
be used to store all of our software. We'll need this system to extremely
stable, because if it goes down no one can get or submit code. With RAID we
could build a single virtual disk (volume) that would meet our need for 200G
of disk. But we also what to make sure that if disks die that we don't go
down. So we use a mirror (another set of disks identical to the first set of
disks). If a disk dies we're okey, because the mirror will take over; we
essentially have 2 identical sets of the same data which are constantly kept
up to date. See? Using these 2 simple RAID concepts we've acheived both
avaliblity (thats our mirror saving us from disk crashes) and increased
capacity (we've got a whole bunch of disks working together, which is
cheaper than buying a single 200G disks... if you can find one!). Okey,
enough of the bad examples. Lets look at the diffrent forms of RAID in use
today. RAID: The Details. ------------------ RAID Type: Concatination
Concatinations are also know as "Simple" RAIDs. A Concatination is a
collection of disks that are "welded" together. Data in a concatination is
layed across the disks in a linear fashion from on disk to the next. So if
we've got 3 9G (gig) disks that are made into a Simple RAID, we'll end up
with a single 27G virtual disk (volume). When you write data to the disk
you'll write to the first disk, and you'll keep writing your data to the
first disk untill it's full, then you'll start writing to the second disk,
and so on. All this is done by the Volume Manager, which is "keeper of the
RAID". Concatination is the cornerstone of RAID. Now, do you see the problem
with this type of RAID? Because we're writting data linearly across the
disks, if we only have 7G of data on our RAID we're only using the first
disk! The 2 other disks are just sitting there bored and useless. This
sucks. We got the big disk we wanted, but it's not any better than a normal
disk drive you can buy off the shelves in terms of performance. There has
got to be a better way.......... RAID Type: Striping (RAID-0) Striping is
similar to Concatination because it will turn a bunch of little disks into a
big single virtual disk (volume), but the difference here is that when we
write data we write it across ALL the disks. So, when we need to read or
write data we're moving really really fast, in fact faster than any one disk
could move. There are 2 things to know about RAID-0, they are: stripe width,
and columns. They sound scary, but they're totally sweet, let me show you.
So, if we're going to read and write across multiple disks in our RAID we
need an organized way to go about it. First, we'll have to agree on how much
data should be writen to a disk before moving to the next; we call that our
"stripe width". Then we'll need far kooler term for each disk, a term that
allows us to visualize our new RAID better..... "column" sounds kool!
Alright, so each disk is a "column" and the amount of data we put on each
"column" before moving to the next is our "stripe width". Let's solidify
this. If we're building a RAID-0 with 4 columns, and a stripe width of 128k,
what do I have? It might look something like this: Look good? So, when we
start writing to our new RAID, we'll write the first 128k to the first
column, then the next 128k to the second column, then the next 128k to the
third column, then the next 128k to the fourth column, THEN the next 128k to
the first coumn, and keep going till all the data is writen. See? If we were
writing a 1M file we'd wrap that one file around all 4 disks almost 3 times!
Can you see now where our speed up comes from? SCSI drives can write data at
about (depending on what type of drive and what type of SCSI) 20M/s. On our
Striped RAID we'd be writting at 80M/s! Kool huh!? But, now we've got
ANOTHER problem. In a Simple RAID if we had, say, 3 9G disks, we'd have 27G
of data. Now, if I only wrote 9G of data to that RAID and the third disk
died, so what, there is no data on it. (See where I'm going with this?) We'd
only be using one of our three disks in a simple. BUT, in a Striped RAID, we
could write only 10M of data to the RAID, but if even ONE disk failed, the
whole thing would be trash because we wrote it on ALL of the disks. So, how
do we solve this one? RAID Type: Mirroring (RAID-1) Mirroring isn't actually
a "RAID" like the other forms, but it's a critical componant to RAID, so it
was honored by being given it's own number. The concept is to create a
seperate RAID (Simple or RAID0) that is used to duplicate an exsisting RAID.
So, it's literally a mirror image of your RAID. This is done so that if a
disk crashes in your RAID the mirror will take over. If one RAID crashes,
then the other RAID takes its place. Simple, right? There's not much to it.
However, there is a new problem! This is expensive... really expensive.
Let's say you wanted a 27G RAID. So you bought 3 9G drives. In order to
mirror it you'll need to buy 3 more 9G drives. If you ever get depressed
you'll start thinking: "You know, I just shelled out $400 for 3 more drives,
and I don't even get more usable space!". Well, in this industry we all get
depressed alot so, they thought of another kool idea for a RAID...... RAID
Type: Stripping plus Mirroring (RAID-0+1) When we talk about mirroring
(RAID-1) we're not explicitly specifying whether we're mirroring a Simple
RAID or a Striped (RAID-0) RAID. RAID-0+1 is a term used to explicitly say
that we're mirroring a Striped RAID. The only thing you need to know about
it is this... A mirror is nothing more that another RAID identical to the
RAID we're trying to protect. So when we build a mirror we'll need the
mirror to be the same type of RAID as the original RAID. If the RAID we want
to mirror is a Simple RAID, our mirror then will be a Simple RAID. If we
want to mirror a Striped RAID, then we'll want another Striped RAID to
mirror the first. Right? So, if you say to me, we're building a RAID-0+1, I
know that we're going to mirror a Striped RAID, and the mirror itself is
going to be striped as well. You'll see this term used more often than
"RAID-1" simply because a mirror, in and of itself, isn't useful. Again,
it's not really a "RAID" in the sense that we mean to use the word. RAID
Type: RAID-5 (Striping with Parity) RAID-5 is the ideal solution for
maximizing disk space and disk redundancy. It's like Striping (RAID-0) in
the fact that we have columns and stripe widths, but when we write data two
interesting things happen: the data is writen to multiple disks at the same
time, and parity is writen with the data. Okey, let's break it down a bit.
Let's say we build a RAID-5 out of 4 9G drives. So we'll have 4 columns, and
lets say our stripe width is 128k again. The first 128k is writen on disks
one, two AND three. At the same time it's writen a little magic number is
written on each disk with the data. That magic number is called the parity.
Then, the second 128k of data is writen to (watch carefully) disks two,
three and four. Again, a parity number is writen with that data. The third
128k of data is written to disks three, four and one. (See, we wrapped
around). And data keeps being written like that. Here's the beauty of it.
Each peice of our data is on three different disks in the RAID at the same
time! Let's look back at our 4 disk raid. We're working normally, writing
along, and then SNAP! Disk 3 fails! Are we worried? Not particularly.
Because our data is being written to 3 disks per write instead of just one,
the RAID is smart enough to just get the data off the other 2 disks it wrote
to! Then, once we replace the bad disk with a new one, the RAID "floods" all
the data back onto the disk from the data on the other 2 adjacent disks!
But, you ask, how does the RAID know it's giving you the correct data?
Because of our parity. When the data was written to disk(s) that parity was
written with it. We (actually the computer does this automatically) just
look at the data on disks 2 and 4, then compare (XOR) the parity written
with the data and if the parity checks out, we know the data is good. Kool
huh? Now, as you might expect, this isn't perfect either. Why? Okey, number
1, remember that parity that saves our butt and makes sure our data is good?
Well, as you might expect the systems CPU has to calculate that, which isn't
hard but we're still wasting CPU cycles for the RAID, which means if the
system is really loaded we may need to (eek!) wait. This is the "performance
hit" you'll hear people talk about. Also, we're writting to 3 disks at a
time for the SAME data, which means we're using up I/O bandwidth and not
getting a real boost out of it. RAID Comparision: RAID0+1 vs RAID5 There are
battles faught in the storage arena, much like the old UNIX vs NT battles.
We tend to fight over RAID0+1 vs RAID5. The fact is that RAID5 is
adventagous because we use less disks in the endevor to provide large
ammounts of disk space, while still having protection. All that means is
that RAID5 is inexpensive comparied to RAID0+1 where we'll need double the
ammount of disk we expect to use, because we'll only need a third more disks
rather than twice as many. But, then RAID5 is also slower than RAID0+1
because of that damned parity. If you really want speed, you'll need to bite
the bullet and use RAID0+1 because even though you need more disks, you
don't need to calculate anything, you just dump the data to the disks. In my
estimates (this isn't scientific, just what I've noticed by experience)
RAID0+1 is about 20%-30% faster than RAID5. Now, in the real world, you
rarely have much choice, and the way to go is clear. If you're given 10 9G
disks and are told to create a 60G RAID, and you can't buy more disks,
you'll need to either go RAID5, or be unprotected. However, if you've got
thoughs same disks and they only want 36G RAID you can go RAID0+1, with the
only drawback that they won't have much room to grow. It's all up to you as
an admin, but always take growth into account. Look at what you've got,
downtime avaliblity to grow when needed, budget, performance needs, etc,
etc, etc. Welcome to the world of capacity planning! RAID History: The Lost
Brothers ------------------------------- Wondering what ever happened to
RAID-2, RAID-3, and RAID-4? You can look in history books for the details,
but they were to be hibrids of mirroring and striping. Ways to include a
parity with the data, for protection, but still staying away from mirroring
each disks in a normal "one-to-one" mirror. One RAID type would have
problems, so they would build another. RAID5, if you hadn't guessed, was the
agreed apon solution. RAID-2 and RAID-3 died and burned and scattered into
the sea of obsolution. However, RAID-4 found a home with our friends at
NetApp (www.netapp.com). See, RAID-4 is faster than RAID-5 because the
parity is writen to a dedicated disk, rather than scattered around with the
data. If you had 4 disks, you'd have 3 data disks, and 1 parity disk. But
what happens if you loose your parity disk? You've lost all protection.
There is no parity, and therefore no way to calculate the data you lost,
meaning that if any of the actual data disks die, your hosed. For this
reason RAID4 is considered dangerous and isn't used. However, NetApp found a
way to make this work and is used in their WAFL filesystem for their product
line of NetApp Filer's (tm), and NetCache's (tm). This is one of the reasons
NetApp's are as fast as they are, RAID-4 is the technology behind it. (It's
unfortunate, but NetApp Filer's are the worlds fastest NFS servers. But one
day Sun is going to kick their ....... never mind.) Conclusion: Closing
Notes ------------------------- Hopefully this all helps a bit. Even if you
didn't know anything about RAID, you should now understand the different
types of RAID and be able to make descisions about what you can do with one
and in which cases each are useful. This is only the very, very begining.
Now it's time to talk Volume Managers, the mechinism by which all this comes
together and works for us. In our next course, we'll learn about the Veritas
Volume Manager in particular. Be aware that Veritas isn't the only Volume
Manager out there, there is also Sun Solstice DiskSuite, Sun RAID Manager,
and others that I don't even know the names of. This isn't enough
information, though. When you choose a volume manager, the documentation
will almost always talk about RAID types in detail. This course you've just
read is simply a diffrent style of explantion which I've found is better
than most others. Here are some links to other places that explain RAID
concepts: SunWorld (www.sunworld.com) - Artical: "0, 1, 0+1 ... RAID basics,
Part 1" - URL: http://www.unixinsider.com/swol-06-1999... -
Note: This article (on SunWorld) is really good. It's part 1 in a 4 part
series. I _highly_ recommend that you read 'em. SystemLogic - Artical:
"RAID: An In-Depth Guide To RAID Technology" - URL:
http://www.systemlogic.net/articles/01/...

Upam, da ti je stvar zdej bol jasna.
Pozdrav_____________________M.

sto ljudi , sto čudi

To je neki za mrčes pobijat - za mravlje še posebej!!!!