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Software Raid.. experiences and thoughts

N

NerdzRule7

Limp Gawd
Joined
Oct 3, 2002
Messages
244
alright heres the deal. i'm setting up a software raid 5 setup soon using 3, 200gb seagates. i was wondering if anyone had real good or real bad experiences with it. from my friend who uses it hes said nothing but good about it so far, just wondering what everyone else on [H]ardforums as to say about it. also, if you have used it before, what os did you use? i'm torn right now between linux and windows. i know linux well, i already use it on my file server, but i know windows better. honestly, in my dual boot win2k and slack 9.1 system i prolly use linux more, just because theres no need to boot into win 2k but i'm wondering if the software raid is easier or better in one or the other.thanks-The_Nerd
 
software raid5 performance will differ among your hardware.
as for me, i tried raid5 w/ 3 200gb (WD SE) using a shitty promise 100tx on a dual xeon 500.

Performance was horrible... max of 2mb/sec writes. (the controller itself drained the cpu like hell so there were little cpu left for parity calculations.

it was (and still is) a linux box.

then i went and did hardware raid5, but thats another story ;)



so if you have beefy hardware, i am sure your raid5 will perform great,
 
for not much more you could do raid0+1 on 4 drives, and get the same capacity, and much better performance. raid5 in software is a last resort, because a) it stresses the processor lots and b) it requires data to cross the pci bus (yuck) twice (double yuck).

a promise tx4000 or something similar would be a better bet, or like i said get another drive and go 0+1.

 
Avoid software RAID at all costs, unless you just simply cannot afford a RAID controller even in the near future. I've played with software RAID on both Windows and Linux/FreeBSD with IDE and SCSI disks and must say that IDE drives with software RAID usually gives very poor performance and even in RAID 5 you'll run a higher risk of loosing data since there are more weak links. With SCSI drives performance improves but the CPU still gets hit doing all the parity information which hurts performance. After playing with software RAID I now run a 324 GB SCSI RAID 5 using 11x36 GB disks (-1 for parity and -1 for hotspare) on an Adaptec RAID card and the performance is great, and thus far (knock on wood) there have been no reliability issues which I've seen a lot of with software RAID. If you do go that route then definatly use Linux as the implementation and reliability is much better than Windows'.
 
my reasons for going software raid are price somewhat. my current server has only 32bit pci slots.. so i could afford the nice promise raid 5 controller all fine and dandy.. then as soon as i put it in, i'll saturate my pci bus so fast my head will spin lol. i was planning on setting it all up on something like an AXP 1600+ and a few highpoint ata controllers, i'm not sure if that would be enough power for it or not, what do you guys think? should i go the extra mile and buy a $200 board with 64bit pci then the raid card? or should i stick with software raid for what i'm doing. basically, i'm just hosting files over my LAN, but its a gigabit network and i'd like to see some decent read/write speeds from the array. i have so much um.. stuff ;) i just had to setup a seperate comp for all my data and now i'd like a little safety for my data.thanks-The_Nerd
 
The general rule for these things is never ask software to do hardware's job. As mentioned about software RAID would make my list of Top 5 Useless Features. Avoid it at all costs. If your not going with a full fledged SCSI RAID5 setup, then there's nothing wong taking your IDE drives and running them in RAID1 if your data is absolutely critical. Since this is not a business critical setup, I would even vote to not use RAID at all. There have been several articles now shoing that in real world usage, RAID arrays (desktop, IDE kind) don't offer any more performance.
 
unhappy_mage said:
for not much more you could do raid0+1 on 4 drives, and get the same capacity, and much better performance. raid5 in software is a last resort, because a) it stresses the processor lots and b) it requires data to cross the pci bus (yuck) twice (double yuck).

a promise tx4000 or something similar would be a better bet, or like i said get another drive and go 0+1.
Click to expand...

raid 0+1 will not give you the same capacity as raid 5 with the same number of disks. With 4+80 gig drives rad 0+1 will give you 160 gig because you lose two drives to mirroring, and with the same drives on raid 5 you will get 240 gig as you only lose the equivalent of one drive to parity.
 
works great
14 18gb 7.2k SCSI LVD hd's on 2 chanel external U80 lvd adaptec card
using windows XP PRO to get spaned 250gb volume with very very excelent transfer rates and a good office heater
 
defakto: i know 0+1 won't be the same capacity as 5 with 4 disks, but it will be cheaper and more effective, especially if your ide controller doesn't go over pci. 4 disks will also give you 2 redundant disks as opposed to 1. since a disk is probably cheaper than a controller, it's a good way to go.
linux software raid0/raid1 are plenty fast. i have a raid0 (shudder) setup with 2 60gb drives, and even though it's a pIII-450, it still gets 60+mb/s i/o. heck, the memory bandwidth isn't much better than that. :(
tdg: more weak links? a hardware raid card is just one big weak link. software raid, you can change motherboards or ide controllers and the array will still work. agreed tho thatraid5 is fine in hardware but should just be skipped in sw.

nerdzrule7: if you can afford a 64bit pci mobo, that's the way to go. then get a 3ware card (sata) and a coupla sata disks. it'll be $2 or $3k but it'll be worth it.
 
PuniPuni said:
Performance was horrible... max of 2mb/sec writes. (the controller itself drained the cpu like hell so there were little cpu left for parity calculations.

it was (and still is) a linux box.
Click to expand...

Just FYI those Promise 100xx cards have a chipset bug in them that drops write speeds to 1-2MB/s when the target drives are on seperate channels and you don't use Promise Win32 drivers. IT took me months to find this out on the FreeBSD lists; had a Promise 100FT with a couple drives in RAID1 on seperate channels when it was presenting the symptoms. Moving both drives to one channel eliminated the problem, though I can still recreate it by hooking up three or four drives and then writing to all simultaneously. Promise won't say what exactly is wrong, so no OSS drivers can get the workaround they use up and running. The card is presently acting as desk clutter.
 
hmm alright. so it sounds like if i should get the new mobo either way, which will give me better bandwidth whichever route i choose. at that point, mabye i'll try software raid in linux first, then if it doesnt preform where i want it to, i'll go to hardware. if anyone has any really swaying evidence then post it please, but it sounds like software raid would do what i need it to do without the extra cash. i'll keep looking into it and thanks again. when i finally get the setup working.. i'll post my own experience to see how everything turned out. thanks again guys-The_Nerd
 
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