RAID: how does it really work?

[imabs]

http://www.onnto.com.tw/product.asp?sys_sysno=23

we have this unit in the office for data storage of finished video projects. since 1 Tb external drives became insufficient to store incoming HD video projects, they've decided to get this to remove all redundant files and finished projects in this hardware.

and this is my first time to understand how does RAID 5 works. it has 4 x 2Tb drives.
my questions would be:
if ever one of the drives are full, can we pull it out and replace a new drive? will there be any data corruption if we insert a new drive?

thanks for giving me understanding on RAID drives.

question on RAID drives
i have read the contents here. but i want to know more based from your experiences.

http://bugclub.org/beginners/hardware/raid.html
thanks for sharing this, theNerve

[bacchus_3]

@imabs, RAID 5 is a block level stripping RAID system - read here http://en.wikipedia.org/wiki/RAID

Think of saving the text "HALO" on your RAID5 system. The letters H-A-L-O is split across each drive. Drive 1 has 'H', Drive 2 has 'A', Drive 3 has 'L' and Drive 4 has 'O'. It does that to all your files. This is just an illustration but it does this to the bit level (smallest form of data storage size for computers).

It will never happen that one of your HDDs will get full first. All drives occupy the same size of data at the same time. RAID5 is used for storage redundancy and avoid data-corruption when 1 drive fails.

RAID 5 uses your 4 x 1 TB HDDs as one virtual 1TB drive. If one of those 4 HDDs fails for any reason you can pull out that one drive and find a replacement. While looking for a replacement the 1TB virtual drive is still available for you to use. It allows you to have 100% availability even on drive failures. It's also faster than a normal 1TB drive.

[imabs]

my understanding is clear and confirmed. thanks bacchus_3.

[raypin]

mmm....just to add to the excellent explanation, if the files are mission-critical and of substantial value, your company might consider off-site, networked storage. RAID is an excellent choice but for one thing: it is still vulnerable because of it stored in one location. Cloud storage for enterprise may be an option and it terminates this threat.

[bacchus_3]

^^ agree with raypin. A lot of people mistake the RAID system as a backup system. It's not. It's a redundancy system only.

[imabs]

that was my suggestion to them in the first place, to set up an independent storage network where an old PowerMac G5 can serve as a server and all external drives are connected to it and accessed thru LAN into Mac workstations.

[anchorite]

if ever one of the drives are full, can we pull it out and replace a new drive? will there be any data corruption if we insert a new drive?

Quick and dirty answer: What ever you do, do not pull your drives out from your array unless it is defective or you are replacing it. Set your array to 3 drives and 1 hotspare. No data is stored in the hotspare. If 1 of the 3 drives fail, your array will go into a 'degraded' mode and will begin populating the hotspare. The array will use your hotspare until you replace the defective drive.

Raid5 only allows 1 failed drive. If a drive fails, replace it immediately. Do not wait. If 2 drives fail, no matter how many members your array has, your data is toast.

BTW, all RAID5 array members MUST be of the same size (to be safe, use the same brand and model). You cannot mix drives with different capacities.

[imabs]

thanks, guys for your inputs.

[cybersniper]

one thing to remember though,

if one member of the RAID system fails, bye bye data...

needless to say, back-up is very critical.

[anchorite]

if one member of the RAID system fails, bye bye data...

needless to say, back-up is very critical.

Hi cybersniper.

That is the case for Raid0. Avoid Raid0 unless you will use it in conjunction with another raid level (Raid0+1).