RAID as a backup system?

On Sat, 5 Jul 2003 12:11:25 +0200
"SMN" wrote:

I know that a RAID system normally isn't a replacement for a
traditional backup system, and that RAID primarily are used to
increase performance and to protect against hard drive breakdown. So
my question might seem a bit odd or stupid.



My problem is that we are administrating a system that needs to run
24/7. We wish to backup the system regularly to protect against data
loss caused by fire or theft. Backup of the data takes approx two
hours, which means two hours of downtime, which isn't an option. Our
software is writing to a relational database consisting of several
database files where file locking isn't allowed.

If you're writing and the records are not locked then you're in trouble
already.

A traditional backup
solution is therefore not an option for us.

If you are using one of the major database managers (Oracle, db2,
Sybase, MS SQL Server, etc) then you should be able to find a backup
solution that supports record locking. Check with the vendor for your
database manager and see what they recommend.

Now I was wondering if it
in any way were possible to use a RAID system where one of the discs
was replaced every week. The removed disk should then be placed in a
safe at another location. This requires of course that the disc can be
removed in such a manner that it is known to contain 100% valid data.
(A downtime of the system of approx 10 minutes during the swap can be
allowed to ensure that data isn't written/updated during the swap). I
am primarily thinking about a RAID-1 system with a hot spare
configuration. Does anybody know if this is possible with any RAID
systems? And if so which?

Any hardware RAID (note--"hardware RAID" means that there is a
dedicated processor on the RAID controller--many devices that
claim to be "hardware RAID" in fact only implement part of the
RAID controller in hardware--with IDE go with 3Ware, with SCSI LSI
Logic, which subsumes both Mylex and AMI--should be
able to do this. No need to take the system down, just dismount the
drive--the RAID controller won't write to it during the dismount--swap
it out, and rebuild the RAID. You'll take a performance hit while it's
rebuilding.

Any help/information will be greatly appreciated.

While a weekly backup is better than no backup, can you afford to lose a
week's transactions?


-

SMN






--
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Go look at Dell and Compaq/HP servers which have hot-swapping RAID drives.


"SMN" wrote in message
...
I know that a RAID system normally isn't a replacement for a traditional
backup system, and that RAID primarily are used to increase performance
and
to protect against hard drive breakdown. So my question might seem a bit
odd
or stupid.



My problem is that we are administrating a system that needs to run 24/7.
We
wish to backup the system regularly to protect against data loss caused by
fire or theft. Backup of the data takes approx two hours, which means two
hours of downtime, which isn't an option. Our software is writing to a
relational database consisting of several database files where file
locking
isn't allowed. A traditional backup solution is therefore not an option
for
us. Now I was wondering if it in any way were possible to use a RAID
system
where one of the discs was replaced every week. The removed disk should
then
be placed in a safe at another location. This requires of course that the
disc can be removed in such a manner that it is known to contain 100%
valid
data. (A downtime of the system of approx 10 minutes during the swap can
be
allowed to ensure that data isn't written/updated during the swap). I am
primarily thinking about a RAID-1 system with a hot spare configuration.
Does anybody know if this is possible with any RAID systems? And if so
which?



Any help/information will be greatly appreciated.



-

SMN

"J.Clarke" wrote in message
t...

On Sat, 5 Jul 2003 12:11:25 +0200

"SMN" wrote:





My problem is that we are administrating a system that needs to run

24/7. We wish to backup the system regularly to protect against data

loss caused by fire or theft. Backup of the data takes approx two

hours, which means two hours of downtime, which isn't an option. Our

software is writing to a relational database consisting of several

database files where file locking isn't allowed.



If you're writing and the records are not locked then you're in trouble

already.

That is true, and we are using record locking. What I meant was that we can'
t allow a backup program to lock files during backup. Moreover if the
integrity of the database backup should be maintained it requires that a
"snap shot" be taken of all the database files, which isn't possible with
traditional tape backup software.


A traditional backup

solution is therefore not an option for us.



If you are using one of the major database managers (Oracle, db2,

Sybase, MS SQL Server, etc) then you should be able to find a backup

solution that supports record locking. Check with the vendor for your

database manager and see what they recommend.

Well the database is build upon DBASE 5. I haven't heard about any backup
solutions for this kind of database.



Now I was wondering if it

in any way were possible to use a RAID system where one of the discs

was replaced every week. The removed disk should then be placed in a

safe at another location. This requires of course that the disc can be

removed in such a manner that it is known to contain 100% valid data.

(A downtime of the system of approx 10 minutes during the swap can be

allowed to ensure that data isn't written/updated during the swap). I

am primarily thinking about a RAID-1 system with a hot spare

configuration. Does anybody know if this is possible with any RAID

systems? And if so which?



Any hardware RAID (note--"hardware RAID" means that there is a

dedicated processor on the RAID controller--many devices that

claim to be "hardware RAID" in fact only implement part of the

RAID controller in hardware--with IDE go with 3Ware, with SCSI LSI

Logic, which subsumes both Mylex and AMI--should be

able to do this. No need to take the system down, just dismount the

drive--the RAID controller won't write to it during the dismount--swap

it out, and rebuild the RAID. You'll take a performance hit while it's

rebuilding.

When you say dismount do you then mean that it normally is possible to
dismount a disk in an RAID array by software at any time?

I am currently looking at a FastTrax TX2000 from Promise
http://www.promise.com/product/datas...p?productId=88. Does
anybody have any experience with that? Is it possible to dismount drives as
described? I have read through the manual and it leaves me a little insecure
about whether it is possible or not.





Any help/information will be greatly appreciated.



While a weekly backup is better than no backup, can you afford to lose a

week's transactions?



Well it's a question on calculating the risk. The probability for data loss
caused by a failed drive will be pretty small if a RAID system is used. It
will only be during the rebuild process that data can be lost. The reason
why we want to store a hard drive in a safe every week is to protect against
theft or fire, which in itself is highly unlikely to take place at the
location. If either fire or theft should take place then we would have to
live with loosing one week of data.

-

SMN

On Sun, 6 Jul 2003 10:43:48 +0200
"SMN" wrote:



"J.Clarke" wrote in message
t...

On Sat, 5 Jul 2003 12:11:25 +0200

"SMN" wrote:





My problem is that we are administrating a system that needs to
run

24/7. We wish to backup the system regularly to protect against
data

loss caused by fire or theft. Backup of the data takes approx two

hours, which means two hours of downtime, which isn't an option.
Our

software is writing to a relational database consisting of several

database files where file locking isn't allowed.



If you're writing and the records are not locked then you're in
trouble

already.

That is true, and we are using record locking. What I meant was that
we can' t allow a backup program to lock files during backup. Moreover
if the integrity of the database backup should be maintained it
requires that a"snap shot" be taken of all the database files, which
isn't possible with traditional tape backup software.


A traditional backup

solution is therefore not an option for us.



If you are using one of the major database managers (Oracle, db2,

Sybase, MS SQL Server, etc) then you should be able to find a backup

solution that supports record locking. Check with the vendor for
your

database manager and see what they recommend.

Well the database is build upon DBASE 5. I haven't heard about any
backup solutions for this kind of database.

Now there's a name I have not heard in many a year. dBase wasn't really
designed for 24/7 mission critical stuff and even the current producers
of that product recommend migrating to an SQL engine under that
circumstance.

If that's not possible though, take a look at "Open File Manager"
http://www.stbernard.com/products/ofm/products_ofm.asp. Also go over
to http://www.dbase.com and take a look in their forums--search on
"backup" and you'll find quite a few hits.



Now I was wondering if it

in any way were possible to use a RAID system where one of the
discs

was replaced every week. The removed disk should then be placed in
a

safe at another location. This requires of course that the disc
can be

removed in such a manner that it is known to contain 100% valid
data.

(A downtime of the system of approx 10 minutes during the swap can
be

allowed to ensure that data isn't written/updated during the
swap). I

am primarily thinking about a RAID-1 system with a hot spare

configuration. Does anybody know if this is possible with any RAID

systems? And if so which?



Any hardware RAID (note--"hardware RAID" means that there is a

dedicated processor on the RAID controller--many devices that

claim to be "hardware RAID" in fact only implement part of the

RAID controller in hardware--with IDE go with 3Ware, with SCSI LSI

Logic, which subsumes both Mylex and AMI--should be

able to do this. No need to take the system down, just dismount the

drive--the RAID controller won't write to it during the
dismount--swap

it out, and rebuild the RAID. You'll take a performance hit while
it's

rebuilding.

When you say dismount do you then mean that it normally is possible to
dismount a disk in an RAID array by software at any time?

Depends on the product, but with enterprise-level stuff yes, it's
generally possible. The intent is to allow graceful replacement of a
failing drive.

I am currently looking at a FastTrax TX2000 from Promise
http://www.promise.com/product/datas...p?productId=88.
Does anybody have any experience with that? Is it possible to dismount
drives as described? I have read through the manual and it leaves me a
little insecure about whether it is possible or not.

Promise products are consumer-oriented. They're trying to change that
but they're not making a lot of progress. Some do support hot-swap but
I don't think the TX2000 is one of them. For IDE RAID take a look
athttp://www.3ware.com. The Adaptec 4-channel IDE RAID products also
work, but the performance of the ones for which I've seen tests is not
as high as for 3ware.

If you are going to be using IDE drives, you'll also need special drive
enclosures that support hot-swapping--IDE drives are not designed to be
used in this fashion and so need some external add-ons to allow it.
Serial ATA drives do support hot-swap but again to do it gracefully with
current hardware you'll need a special enclosure, otherwise you're going
to be dealing with plugging and unplugging cables. Promise and 3ware
sell enclosures made for this purpose.

A good backplane-based SCSI solution you'll find to be a lot more
graceful. A Poweredge 2600 suitably fitted should do everything you
need--just make sure you get however many extra drive-carriers you
need--the carriers are just an open frame and a latch.

Don't expect any solution to be cheap.

Also, whatever you do, _test_ it and make sure that you can actually get
the data back. After the fire is not the time to find that your backup
strategy is flawed.

Any help/information will be greatly appreciated.



While a weekly backup is better than no backup, can you afford to
lose a

week's transactions?



Well it's a question on calculating the risk. The probability for data
loss caused by a failed drive will be pretty small if a RAID system is
used. It will only be during the rebuild process that data can be
lost. The reason why we want to store a hard drive in a safe every
week is to protect against theft or fire, which in itself is highly
unlikely to take place at the location. If either fire or theft should
take place then we would have to live with loosing one week of data.

-

SMN




--
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)