Hi, bettablue.
I am left still with a nagging question about RAID in general.
While I'm sure others can explain RAID better, here's my non-techie and
greatly-simplified stab at it.
RAID 0 is striping. That means that a program gets divided into pieces
called "stripes" and written to two disks. Step 1 of the program goes to
the first disk, Step 2 to the second disk, Step 3 back to the first, etc.
Since each of the two disks has its own set of read/write heads, Step 1 and
Step 2 can be written simultaneously, so it takes only half as long to write
the whole program - plus a small amount of overhead. Only one copy of each
step is stored, so there is no wasted space.
RAID 1 is like a mirror. The means that a data file is written twice. Data
Item 1 is written to the first disk, and then written also to the second
disk. Again, because each disk has its own set of read/write heads, the two
writes take only slightly longer than a single write. There is no time
saving with RAID 1; a thousand items will take just as long - or slightly
longer - than using a single non-RAID disk. Since each item is stored in
two places, this uses twice as much disk space. (While each datum is
written twice, I don't think it is read twice each time it is needed.)
Since both RAID methods typically use two identical disks with equal risk of
failure (MTBF), there is about twice the risk that ONE of the two disks will
fail while the other continues to function. The effects of a single-disk
failure are quite different between RAID 0 and RAID 1.
If a RAID 0 disk fails, the operating system will not be able to start or to
load and run programs. No matter how perfectly it loads Step 1 and Step 3
from the good first disk, if it doesn't have Step 2 from the bad second
disk, the program's integrity will not pass muster and the program will
probably not even start.
If a RAID 1 disk fails, the OS should be able to load the entire program or
database from the other identical disk. The RAID program itself should warn
you that the RAID Array has failed, giving you some time to replace the bad
disk and rebuild the array while continuing to operate from the good disk.
So, RAID 0 gives you a speed advantage, while doubling your risk of complete
failure. RAID 1 costs a small time penalty but increases your chances of
surviving SOME types of disk failure. (There are other flavors of RAID, but
let's not get into all that.)
My only experience with RAID started about 3 years ago, after one of my 3
HDDs failed, taking much of my data (photos, etc.) with it. My BIOS had
RAID built-in, so I decided to try it. I replaced that single disk with a
pair of identical 300 GB Seagate Barracudas. After a lot of stumbling and
fumbling with new terminology, I recreated my "lost" data folders, then
rescued and copied as much as I could to one of the new disks. Then I
plugged in the second and let the system "build the array", which took about
a day, working mostly in the background while I continued to work in the
foreground. The RAID mirror has worked with almost no maintenance since
those first few adventurous weeks.
Disk Management sees my HDDs as Disk 0 (200 GB), Disk 1 (1 TB) and Disk 3
(300 GB; the TWO 300 GB disks are seen as a single "disk"). Each disk,
including the RAID "disk", is divided into several logical drives and
partitions. Any change in boot-up time has been so small that I don't
really notice. That disk is used mostly for data storage, but there are
several programs that load and run from there, too, and I've seen no
difference in performance or speed from when they were on a single disk.
That means that I have 1.8 TB of physical capacity but Win7 sees only 1.5
TB; I'm giving up 300 GB for the redundancy. This does not protect me from
a theft or fire or other loss of my entire computer, and maybe not from a
lightning strike or other disaster that would damage both disks. And a
program glitch could still write garbage to both disks. I still need to
backup my most critical data. But simple failure of one disk - as has
happened to me more than once - will not cost me the mirrored data. I'll
just replace the bad disk and rebuild the array. There is still some risk
of data loss, but it has been reduced to a level that I can live with.
I'm not bold enough yet to use RAID 0. But RAID 1 is working well for me.
RC
--
R. C. White, CPA
San Marcos, TX
(e-mail address removed)
Microsoft Windows MVP
Windows Live Mail 2010 (15.3.2804.0607) in Win7 Ultimate x64)
"bettablue" wrote in message
Bill Bradshaw said:
As somebody who runs raid 1 follow the advice here and backup. Raid 1
basically keeps duplicate drives so if your primary gets garbage written
to it so will your secondary and you end up with two trashed drives.
All great advice... And, I personally do use regular backups to make sure I
am not losing anything important.
I am left still with a nagging question about RAID in general. I understand
that using it as a backup solution is probably not the way to go, however,
what about using RAID to speed the operation of the PC's operation and boot
loading? Looking at my Windows 7 performance numbers, I see that my primary
hard disk is the lowest scoring item at 5.9 while all of the other
performance parameters read at least 6.5. Will setting up a RAID array
speed up system performance? I mean, with 2 disk drives operating as one,
the theoretical boost in read/write performance would seem to double just
for the fact that you would essentially have double the disk cache and
buffer size.
