[Headcase_Fargon]

Software raid 5 takes up a lot of overhead as it writes its parity across 3 or 5 drives. If you use 3 drives of all the same sizes, you will lose 1. If you use 5 drives, you will lose 20%. To rebuild a software raid 5 can take days if one of the drive fails. Let's not get into detail if the motherboard fails, you will need to find the similar chipset (Intel ICH10R) or something to make sure you can rebuild your storage pool.

In hardware raid 5, you just take the card out and put it into a different Mobo and your array will start to work immediately. Rebuilding the array with hardware raid 5 is hours, vs days.

Write speed on software raid 5 can vary but I've heard as low as 10mb per sec up to a max of 15-17mb.

I was curious about this statement so I asked the folks on HardForum what sort of performance I might expect with an mdadm (software) RAID under Ubuntu and they said 130MB/sec at least. They say it's very efficient with modern processors.

I think I'll give it a shot.

[r1lee]

Make sure they are not referring to read speed but writes. I call BS on a 130mb write. Unless its a burst.

You should read these
http://communities.intel.com/message/106449
http://communities.intel.com/thread/11020
http://forums.anandtech.com/showthread.php?t=2176185

Rebuilding an array if 1 drive fails.
66hrs hours to rebuild a 25gb array. Whereas hardware raid5 takes hours.
http://forums.storagereview.com/index.ph...5-rebuild/

Here's another one.
http://forums.techarena.in/small-busines...100942.htm



If you are building a Raid 1 server, then no worries. But the execution of a raid5 is very demanding. Hence the reason people buy $200+ hardware raid cards.

[Kirky99]

I was curious about this statement so I asked the folks on HardForum what sort of performance I might expect with an mdadm (software) RAID under Ubuntu and they said 130MB/sec at least. They say it's very efficient with modern processors.

I think I'll give it a shot.

Here's some results I got when I was running MDADM... Array was RAID 5 (4 x 1TB 7200RPM drives) running on a crappy Athlon II X2 240e CPU (45W 2.8Ghz)

Code:

hdparm -tT /dev/md0
/dev/md0:
Timing cached reads:   4318 MB in  2.00 seconds = 2159.56 MB/sec
Timing buffered disk reads:  826 MB in  3.00 seconds = 275.08 MB/sec

Code:

# dd if=/dev/zero of=test bs=1M count=16384
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 104.25 s, 165 MB/s
# dd if=test of=/dev/null bs=1M
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 63.0578 s, 272 MB/s

The problem was I was getting CPU bound at times, but I knew that was a possibility with the CPU I was getting. It was only a problem when a bluray rip complete in SAB+ and it needed to unrar, etc.

Linux got the best of me though, learning curve was too much for this old coot!

[r1lee]

Basically I want is a Raid 5 or 6 that I can expand as I go. I was thinking something like this http://www.newegg.com/Product/Product.as...6822122010 but I don't think 4 drive bays in raid 5 would be enough especially if I don't compress my Blu-ray movies. 6 sata ports/ hard drives would be enough I think, has anyone had any problems with unraid? how much does it cost?

I would consider not going the Netgear route. In the past, their systems were pretty bad (slow), i can't say how well they fair now.

I would look at Synology and Qnap. Something like this.
http://www.amazon.com/Synology-DiskStati...grid_i_0_1

[Headcase_Fargon]

Here's some results I got when I was running MDADM... Array was RAID 5 (4 x 1TB 7200RPM drives) running on a crappy Athlon II X2 240e CPU (45W 2.8Ghz)

Code:

hdparm -tT /dev/md0
/dev/md0:
Timing cached reads:   4318 MB in  2.00 seconds = 2159.56 MB/sec
Timing buffered disk reads:  826 MB in  3.00 seconds = 275.08 MB/sec

Code:

# dd if=/dev/zero of=test bs=1M count=16384
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 104.25 s, 165 MB/s
# dd if=test of=/dev/null bs=1M
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 63.0578 s, 272 MB/s

The problem was I was getting CPU bound at times, but I knew that was a possibility with the CPU I was getting. It was only a problem when a bluray rip complete in SAB+ and it needed to unrar, etc.

Linux got the best of me though, learning curve was too much for this old coot!

Am I missing something here? 165MB/s sounds pretty outstanding to me.

[Headcase_Fargon]

Make sure they are not referring to read speed but writes. I call BS on a 130mb write. Unless its a burst.

You should read these
http://communities.intel.com/message/106449
http://communities.intel.com/thread/11020
http://forums.anandtech.com/showthread.php?t=2176185

If you are building a Raid 1 server, then no worries. But the execution of a raid5 is very demanding. Hence the reason people buy $200+ hardware raid cards.

The results in your links were in Windows. I'm talking about using mdadm under Linux.

[r1lee]

very difficult to find these ones, but here's one using MDADM.

http://ubuntuforums.org/showthread.php?t=1420703

i can't comment on if they are runnign hardware or software.

you're right, i could be totally off my mark for non-Window PC's. I'm just going by how a software raid array is built. It's not built within the confines of the Windows OS. The OS is just software sitting on top of an Array (volume). Now if the Intel software is bad on how it handles writes and parity checks, and Ubuntu is more efficient, then I don't know.

I can't see Windows effecting write speeds when all its doing is just sitting there.

[Kirky99]

Am I missing something here? 165MB/s sounds pretty outstanding to me.

No, I don't think you're missing anything. I was mostly impressed, and more than adequate for my little home network. I moved away because I needed to implement a TV server and just couldn't get it done on that Linux box. Linux isn't my first language (it's not even my 10th) and just couldn't get it to work.

If you are comfortable, have at it. The only time it caused issues was like I said, when my processor became write bound during a unrar of a file, I would see slight hiccups on a client PC that may have been playing a HD video. Otherwise, I never really knew or cared what was going on with the file server. It just worked...

BTW - That machine is now a Win machine running FlexRAID in a Snapshot RAID configuration. Switched to 4 x 2Tb drives @ 5900 rpm (3DRU, 1PPU) and the parity update runs between 70-90MBs if I recall correctly. The first parity update took about 7.5 hours. Just thought I'd throw that out there, even if it's just for Google to see and index.