The system in my signature uses two drives. The first is a 250 GB SATA for the OS, and a 500GB SATA for the data. I'd like to get another 250GB and another 500GB and put them in two RAID 1's. Can I do this now even though this system is being used??
I'd use the RAID controller on my Gigabyte motherboard unless I need to use something else.
"Can I do this now even though this system is being used?"
You mean can you setup RAID while the system is running? With SATA you can 'hot-plug' the cables, but the RAID BIOS setup utility probably wont support that.
If you meant if it would keep all data intact while creating the RAID1: yes and no. The last sector on the HDD would get overwritten. I'm not sure how windows deals with this.
As a personal note, i recommend to use backups instead, and not RAID1. If you put your backups also on RAID, the same RAID engine as your primary data, both your backup and primary are sharing the same failure point: the RAID layer. This might not be very safe actually.
Without knowing your partition setup, here's what I would do:
(1) create a drive image of your OS partition e.g. C:
and write it to your 500GB
(2) backup any data partition(s) on your 250GB
to your 500GB and possibly to a second HDD e.g. USB external:
your second 500GB would work as a temporary backup
(3) cable your new 250GB and configure the
2 x 250GB as RAID 1
(4) designate that RAID 1 as your boot drive
(5) restore the drive image of your OS partition
to this RAID 1
(6) restore any data partition(s) to this RAID 1
(7) backup all data on your first 500GB
(8) repeat this sequence with your 2 x 500GB
To be safe, I would highly recommend that you also
invest in an external USB drive, and doubly backup
everything, in case something goes wrong.
Hard drives are very cheap now, and the extra expense
is really cheap insurance.
If you're not comfortable with the above sequence,
then buy 2 x new 250GBs, and create the RAID 1
with them. This way, you will be removing your
existing 250GB without making any changes
to that HDD: if you run into trouble, you can
always revert to your existing configuration --
by booting your OS from that existing 250GB.
As a general rule, you should always migrate
your most important files e.g. OS to the newest HDDs,
and demote aging HDDs to a backup role. In this way,
your aging HDDs will last longer because you are not
doing as much I/O with them. Along these lines,
I would also recommend 2 x new 250GBs, using
Western Digital's "RAID Edition" series e.g.:
These enterprise-class HDDs have a longer factory warranty;
thus, price per warranty-year is very favorable over 3-year warranties.
Also, the internal components are superior e.g. perpendicular magnetic
recording is superior to the older horizontal method. And, when building a
RAID 1, both HDDs should be identical in every respect.
Recommendation: buy 2 new 250GB HDDs, like the WD 250GB RE3 above,
instead of 1 x 250 and 1 x 500. You can then demote your existing
250GB to a backup role, and later get a much faster 500GB,
or a pair of identical faster 500GB HDDs for RAID 1 data storage,
as funds permit: