New server - Which raid?

[dave.81]

Well just go a new Dell server which will be taking over from our main DC,dns,dhcp,ranger and users homespace, which is struggling at the moment.

 

Spec is, 2x quad core 2.5ghz, 8gb ram, 4x300gb 15k sas drives.

 

I'm trying to work out which raid setup to give it though, my first thought is using raid 5 with 3 of the drives and then 1 hotspare, or could have all 4 in raid 5.

 

Just cannot decide which one to go with, any ideas on which would be best?

[SYNACK]

If you can't decide at the moment go with the hot spare as it is trivial to expand the array onto it later if you need to. It is much more difficult to remove a drive from a RAID 5 array. If you do not need the space now go with the hot spare which will give you extra fault tolerance and also it will mean (depending on the controller) that the spare will not be spun up and so won't be wearing out in the mean time.

[joe90bass]

You'll probably get lots of different answers on this one!

With our new servers I've tried to go RAID 1 system drive and RAID 5 on the data drive. Where possible I've tried to have a hot swap spare as well. Normally the budget dictates you strip things to the bare minimum, luckily we had the funds to do things properly on this occassion and I could afford to do the above

[richard.thomas]

On the servers i've built i've done the same as Joe. Raid 1 for the OS and Raid 5 for the data

[Michael]

There isn't really a right or wrong answer here. I would probably go for RAID 5 though as it's far more efficient than RAID 1.

[kesomir]

raid 6? (if perc6i)

 

other than that I'd say raid 5 + hot spare.

[DELL-Dennis_S]

Hi Dave

 

All of the recommendations above are great (and you will prob see more). If it were me I would see if I could manage to buy a 5th drive and then have 2 drives for the OS and 3 for the data as suggested by Joe. If this is not possible I would have to lean towards the suggestion of kesomir and go with RAID 6 this is basically RAID 5 but different parity striping, so you can lose 2 drives before failing.

[dave.81]

Thanks all, it is a 6i controller so raid 6 is an option. I might look at getting a 5th drive although the budget for the server is all spent i do have reserves and as everyone has said raid 1 for the OS and raid 5 for data seems to be the common theme.

 

Am i right in thinking as long as the 5th drive is the same speed etc etc it doesn't have to be the same make?

Edited August 21, 2008 by dave.81

[cookie_monster]

There isn't really a right or wrong answer here. I would probably go for RAID 5 though as it's far more efficient than RAID 1.

 

@ Michael: isn't that far more efficient on space rather than performance? RAID 1 and a 3 disk RAID 5 are both using 2 disks to read from (theoretically)

 

 

Am i right in thinking as long as the 5th drive is the same speed etc etc it doesn't have to be the same make?

 

No it doesn't need to be the same make.

Edited August 21, 2008 by cookie_monster

[Geoff]

Again, I'm in the 'Raid 1 for the system drive plus Raid 5 for the data' camp. It's how I've configured my new file server here. I would only consider raid6 if you were using a lot of drives (12+) as that is the point you see tangible benefits.

[dave.81]

Now i'm thinking 300gb for a OS drive is a tad much, think i might get 2 smaller drives, 73gb possibly then use the 4x300gb ones for file storage. I always used to by seagates for my home pc they any good?

 

Thanks again for all the help

[cookie_monster]

Yep Seagate seem to be the biz still when we had no end of Maxtor drives fail in our Dell's they immidiatly started to replace them with Seagate disks (we lost 4 out of 6 Maxtors over 6 months) they really do seem to be very reliable. We seem to of had a few issues with Hitachi disks but that could just of been a bad batch overall most are a decent standard these days.

[Michael]

@ Michael: isn't that far more efficient on space rather than performance? RAID 1 and a 3 disk RAID 5 are both using 2 disks to read from (theoretically)

 

Yes you're correct. Using hardware RAID 5, you can include the OS and all user data. Although you could use RAID 1 it just seems additional work.

 

Am i right in thinking as long as the 5th drive is the same speed etc etc it doesn't have to be the same make?

 

Same make no, but same capacity (yes highly recommended).

 

Now i'm thinking 300gb for a OS drive is a tad much, think i might get 2 smaller drives, 73gb possibly then use the 4x300gb ones for file storage. I always used to by seagates for my home pc they any good?

 

Remember if you setup RAID 5 (lets say you had 5 physical disks) in Windows it would appear as one huge single drive. 300GB x 5 = 1.5TB for everything.

[DMcCoy]

Yes you're correct. Using hardware RAID 5, you can include the OS and all user data. Although you could use RAID 1 it just seems additional work.

 

 

 

Same make no, but same capacity (yes highly recommended).

 

 

 

Remember if you setup RAID 5 (lets say you had 5 physical disks) in Windows it would appear as one huge single drive. 300GB x 5 = 1.5TB for everything.

 

Same or higher capacity will do. Preferably the same rpm too (this is a good idea!). Matched drives is more efficient as all the seek times etc should be the same. Nothing to stop you partitioning the 1.2TB raid volume into sever parts keeping the os and data separate still.

 

RAID 5 really isn't *that* slow, especially when you get more than the minimum of 3 disks.

 

I'm currently using a 12 disk RAID6 group on one san and a 9 disk RAID5 on the other.

 

 

RAID1 for most OS is a bit of overkill if you monitor the disk performance, although it can be nice for a disaster recovery point, although proper backup will mitigate that anyway.

[Midget]

if you can afford it, go RAID10, it's faster and more redundant. If you can't then I guess it's going to have to be RAID5 if you have <6hdds (not worth RAID6 when under that)

 

Just remember RAID0 is called as much because thats how many files you'll get back when it fails.

[tmcd35]

if you can afford it, go RAID10, it's faster and more redundant.

 

Faster yes, more redundant no. Both RAID-5 and RAID-1 offer 1 disk redundancy. Also RAID-10 will have a lower capacity than on RAID-5. If 2 disks go you are screwed. RAID-6 gives 2 disk redundancy as does RAID-50, which should be slightly faster than RAID-6. The redundancy is better on RAID-6 than RAID-5. Hot spares are a very good idea!

 

I have a 12-disk SAN here, 10xRAID-50 + 2xHot Spares = 4 disks can fail before I have to totally panic!

[Midget]

yes RAID10 gives less capacity, but then RAID5 gives less than RAID0

 

Why would you ever allow 2 disk to get screwed? Only idiots would not notice a failed HDD and there is a lower chance of both of the same section of the stripe failing.

 

If 2 disks fail irrepairably in RAID5 then you are done.

 

as we were tlaking about <6HDDs then RAID 6 is a bit useless.