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hightower

Member

Registered: 2006-04-02

Posts: 182

Software RAID requirements and questions

Hi,

As I bought a new harddrive I thought, I could try to build a striping software RAID (RAID 0), in order to gain some speed.

1. Have both harddrives to be partitioned identically, or is it sufficient when both RAID partitions are equal?

2. May the postition of the two partitions differ?

3. Is the gain of speed noticeable in a software RAID?

hightower

eWoud

Member

Registered: 2005-07-06

Posts: 39

Re: Software RAID requirements and questions

As I bought a new harddrive I thought, I could try to build a striping software RAID (RAID 0), in order to gain some speed.

1. Have both harddrives to be partitioned identically, or is it sufficient when both RAID partitions are equal?

2. May the postition of the two partitions differ?

RAID uses the discs in its entirety. Ideally, the drives should be identical.
EDIT: ok I guess it's not really needed for LVM, but recommended for performance reasons.

3. Is the gain of speed noticeable in a software RAID?

Seek time goes up by the tiniest amount (in a bad way), sequential reads (large files) are faster. Reliability goes way down.

Noticable: yes, worth it: no, unless you backup daily.

---

tea is overrated

The_Nerd

Member

From: Syracuse, NY / Baltimore, MD

Registered: 2005-11-30

Posts: 134

Website

Re: Software RAID requirements and questions

1. Have both harddrives to be partitioned identically, or is it sufficient when both RAID partitions are equal?

Only the partitions need to be equal. Software raid can work with full disks, or partitions only. Either or should be fine, though whole disks should yield better performance since the reader head will be dedicated to the RAID. If you have a non-raided partition that gets written to often, and then a RAID 0 lets say home dir, your performance might suffer since you will be trying to write to the RAID parition often, and that will slow any writes to the other partiton, even if it be by a small amount AFAIK.

2. May the postition of the two partitions differ?

Yep no problem here, just make sure you know what paritions are what.

3. Is the gain of speed noticeable in a software RAID?

This I cannot honestly say. I ran RAID 0 in my desktop for years and in some benchmarks found it to be faster, yet in actual computer usage, it seemed slower in some tasks than my other, single harddrive computers. I might try it out for a week before you fully comitt if you can, since you may or may not see a performence difference.

Good luck with whatever you choose!

hightower

Member

Registered: 2006-04-02

Posts: 182

Re: Software RAID requirements and questions

hi,

I ran the badblocks test (read-write) on the new hdd (hdb) and simultaniously I checked the performance of hda, which broke down from ~35MB/s (without operation on hdb) to ~9 MB/s. I think this loss is a result of the two drives sharing one controller, so I think using a RAID is something stupid with this performance.

hightower

The_Nerd

Member

From: Syracuse, NY / Baltimore, MD

Registered: 2005-11-30

Posts: 134

Website

Re: Software RAID requirements and questions

Yea two drives on one controller is a bad idea. If i remember correctly, ATA drives in a Master/Slave configuration get written to and read from in that order Master, then Slave. This would mean that it would have to read a chunk of data, wait, and then read the second chunk of data from the Slave which would be much slower than a single drive alone.

Sorry for not thinking of that before hightower, I'm used to SATA now with only one drive per channel to worry about. :oops: