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Software raid 5.. Is there such a thing in ANY os?
- Thread starter BDSM
- Start date
Okay.. thanx. I'm a novice on this.
Could I have a boot disk without raid and then perhaps four or five drives in the raid array?
Is it possible to add drives to raid 5 array?
Can the drives be on different controllers?
Do they have to be on separate channels?
How much space would I "lose" in a 4 drive array consisting of 4 Deskstar 120 gb drives?
Could I have a boot disk without raid and then perhaps four or five drives in the raid array?
Is it possible to add drives to raid 5 array?
Can the drives be on different controllers?
Do they have to be on separate channels?
How much space would I "lose" in a 4 drive array consisting of 4 Deskstar 120 gb drives?
LiLithTecH
Diamond Member
While they don't have to be on Seperate Channels, if you want it to complete
the synching at some point, you will place them on seperate channels.
If you place them both on the same channel (Pri-master, Sec-slave or Cable Select)
the I/O requests double, slowing down an already painfully slow process.
Software Raid is very, very slow.
You may want to consider purchasing an inexpensive controller card to help your cause.
Highpoint Rocket 133 Raid controller (2 channel) can be had for $20 online.
the synching at some point, you will place them on seperate channels.
If you place them both on the same channel (Pri-master, Sec-slave or Cable Select)
the I/O requests double, slowing down an already painfully slow process.
Software Raid is very, very slow.
You may want to consider purchasing an inexpensive controller card to help your cause.
Highpoint Rocket 133 Raid controller (2 channel) can be had for $20 online.
Nothinman
Elite Member
Software RAID 5 takes a performance hit because the system CPU has to do the parity calculation, if the host isn't doing anything CPU intensive it won't be a big slow down. Software RAID 1 and 0 are just as fast, sometimes faster, than hardware RAID 1 or 0 because there's no additional calculations to be done and the OS can sometimes organize reads and writes to the disks better than a hardware RAID controller, atleast on Linux.
The big benefit to hardware RAID is, usually, the cache on the board. You can get boards with tons of memory ( 128M, 512M, etc) as an added buffer so you don't hit the disks as much and any reputable RAID controller will have a battery backup for the memory so if the power does go out it can write the cache to disk before shutting the drives down.
Since this is just for MP3s and videos why not consider getting a DVD-RW and back them up that way? With any amount of disks you have a chance of any of them failing, RAID 5 only protects you against 1 drive failing so if 2 go you still lose all your data.
LiLithTecH
Diamond Member
On a MS Windows machine IDE Controller & Disks it is very slow.
Compared to a SCSI Raid on a Linux box, it is extremely slow.
I was suggesting an inexpensive alternative, not a $500 Mylex SCSI controller.
This is MY understanding of the various RAID's. (please correct me if I am wrong)
RAID 0 requires a minimum of 2 drives
Implements a striped disk array, the data is broken down into
blocks and each block is written to a separate disk drive
I/O performance is greatly improved by spreading the I/O load across many
channels and drives
Best performance is achieved when data is striped across multiple controllers
with only one drive per controller
No parity calculation overhead is involved
Not a "True" RAID because it is NOT fault-tolerant
The failure of just one drive will result in all data in an array being lost
RAID 1 requires a minimum of 2 drives
One Write or two Reads possible per mirrored pair
Twice the Read transaction rate of single disks, same Write transaction rate as
single disks
100% redundancy of data means no rebuild is necessary in case of a disk failure,
just a copy to the replacement disk
Transfer rate per block is equal to that of a single disk
Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures
Highest disk overhead of all RAID types (100%) - inefficient
Typically the RAID function is done by system software, loading the CPU/Server and
possibly degrading throughput at high activity levels. Hardware raid always is
strongly recommended
May not support hot swap of failed disk when implemented in "software"
RAID 5 requires a minimum of 3 drives
Highest Read data transaction rate
Medium Write data transaction rate
Low ratio of ECC (Parity) disks to data disks means higher efficiency
Good transfer rate
Disk failure has a medium impact on throughput
Most complex controller design
Difficult to rebuild in the event of a disk failure (as compared to RAID level 1)
Individual block data transfer rate same as single disk
Nothinman
Elite Member
Linux software RAID (md) driver has been benchmarked in RAID 1 and RAID 0 configs to be faster than similar configured IDE RAID controllers, RAID 5 speed would be totally dependent on the situation. I'm sure his MP3 and TV video collection is 95% read access, so RAID 5 in software would be fine once the initial build and copy finishes.
Even with IDE a single controller there's 2 interfaces, so you can have 2 drives without them blocking each other. With SCSI each drive disconnects from the chain while it does the transaction and each device can have multiple transactions queued up, so essentially they don't get in each other's way even if they're on the same wire. And a basic SCSI3 controller can handle 15 devices per interface.
Depends on the implementation, sometimes the write time is twice as slow because it waits for both to write to ensure data integrity. But with all the levels of caching on a computer it won't really be twice as slow.
I've not seen a setup that lets you have a single drive with 2 mirrors, although I don't see technically why it can't be done.
There's no real overhead to load on the system, it issues 2 writes per memory page instead of 1, you're still stuck waiting on disk I/O.
A lot of hardware solutions don't support hotswap, especially IDE ones.
Depends. If I have 16 drives in RAID 0 and 16 drives in RAID 5 I bet the RAID 0 set will be faster, all else equal.
Unless you have a spare disk allocated a disk failure means the array is down until you get a replacement, unlike RAID 1.
Should be just as easy as the others, add the new disk and let it rebuild the array.
The individual block transfer rates are the same across the board, you only have a single block on any disk. Unless you're talking about a different measurement than the 'block' I've always used to mean a physical disk sector, i.e. 512 bytes (except on really odd hardware). If you mean filesystem cluster or just 'chunk of data' then yes you're right.
dartblazer
Senior member
i know this is something that is totally different from what you were originally thinking but what about firewire hard drives and backing up to DVD-R? you could do weekly backups to dvd-r, and use catalogging software? seems like a more reliable situation to me.
but if youre looking for a raid 5 ide card, promise makes a nice one, the sx6000 i believe.
but if youre looking for a raid 5 ide card, promise makes a nice one, the sx6000 i believe.
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