Need some advice on backup-to-disk system

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Hello all.

I was wondering if i could get your ideas and advice about a disk system im going to build for my company, mostly for usage as backup system.

its a basic 16 disk system, where i was planning the following configuration:

2x 8506-8 3ware Escalade controllers
16x 250gig disks, either WD or Maxtor
1 or 2 gigs of ram, and a good sized CPU.

My idea is to make an array on each of the controllers like this

Array 1 = Disk 1-7 in Raid5, Disk 8 as hotspare

Array 2 = Disk 9-15 in Raid5, Disk 16 as hotspare

Array 3 = Array 1 and Array 2 in Raid0. (windows 2003 software)


This should give me a theoretical writespeed of around 80MB/s or more, and still keep the security and maximizing the number of disks actually used for storage.

Only weak points i see in it, is a controller failure, or if the software stripeset explodes somehow.

Gentlemen or ladies, what are your thoughts?

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[P5-133XL]

My experiance is that you can't mix 3ware's raid and Microsofts (choose one).

By choosing Raid-0 in your mix, you risk all because if for any reason the Raid-0 array has any problems it will be unrecoverable. Drive failure is only one possible reason for problems and you've covered that but what happens if Windows simply crashes and when it comes back up the array is gone. Raid-0 is very much not recomended

Make sure that the 3ware cards are in advanced PCI slots (preferably PCI-X) because the standard 32x33 PCI is will limit your performance.

Don't expect even close to your theoretical write speed except for benchmarking. Raid-5's write speeds suck and it doesn't really matter how much you try to massage the arrays, by adding raid-0 or adding lots of drives, it will still suck. Also note that accessing the array over a 10/100 network will limit performance to a max theoretical speed of 12.5MB/s and GbE to 125MB/s but realisticly 10.5MB/s and 30MB/s are more likely.

Note, if you are not performance oriented or are limited by network BW constraints then raid-5 is fine. If you are in need of the performance then use raid 10

 

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The biggest problem with Raid 10 is the amount of disk's "wasted" using that method.

As such the data isnt Vital information, since we will make a backup to tape from the server once a week.

My biggest concern is that i run into that pesky 3 TB array limit the controllers have, and i assume two controllers cant "share the load", by that meaning, that i can make one big array over two controllers.

The plan is to have a Intel 1 Gbit MT server dualport card additionally on the server, so i dont run into network bandwith problems, since we need to make 300 GB backup every night, currently we run it on DLT and its very time consuming (take around 36 hours), and its a mess to restore files.

Unfortunately Company policy is such that a differential on incremental backup is not a valid option, so i have to build a disk system with room enough for atleast a weeks backup..

6x300= 1.8TB a week. And for easy management two weeks would be appreciated on my behalf

The raid0 solution is merely there to give me a bigger partition to store the backup files on.

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[P5-133XL]

You are correct that the two 3ware cards can't make a single array. But MS software raid can make a single array from multiple controllers: It doesn't tend to be as stable as a single controller because of timing issues, but it works.

Knowing a little about the background, I'll make some suggestions.

Rather than trying to mix MS and 3wares raid in a raid-0 array. How about hanging the disks off the 3ware as individual disks and simply using MS software raid-5 as a single partition. Here you are simply using the capability of the 3ware cards to hang alot of drives off of them. The drawback here is the loss of the hot-spares: MS software raid does not support hot-spares

Next suggestion is not to use raid or make a single partition at all. Depending upon the capacity of the disks (try Maxtor's 5400RMP 300GB drives) you might be able to fit one backup per drive. If so, then you have two options - You can assign drive letters to the drives and backup monday on drive E:, tuesday on Drive F, ... or you can mount the drives into a directory: You would have a drive E: called backup and directory's monday, tuesday, wednesday.... In either of these situations the performance will be limited by the STR of an individual drive. In these choices the drawback is the speed of the non-arrayed drives may limit you. Also, if your backups don't fit a single drive or if the size of the backups may grow beyond the size of an individual disk then this method is not for you. The benefit is that it is simpler and thereby less likely to fail and if a drive fails, you will loose only that one backup while the others will remain intact and accessible.

Do note with a single GbE card the normal expected maximum transfer rate should be on the order of 30-50MB/s which is actually close to the STR for a modern HD. With a dual port GbE then you can double it when setup with load-balancing.

You are going to have to have a server MB with several PCI-X, 64x33, 64x66, or 32x66 PCI slots because the BW requirement of all the cards working together will be enormous: Far more BW than a single normal 33x32 PCI bus.

 

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Im afraid that, running without any sort of redudancy on the harddrives, is a thing im not willing to risk. and raid 1+0 is not a economical sound solution, too many disks are "lost", i do not need that high performance really, around 10-15MB/S write speed is all i need, that should give me roughly 300GB in 4-5 Hours, probably more than what my old compaq servers can deliver (they all run raid 5's too).

The main issue for me is capacity.. the more the better.. And for Ease of use, one big drive.

and unfortunately the raid controllers, have a 3TB array limitation, so if i want bigger, i need to resolve to software Raid.

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[blakerwry]

marks last solution seems to have the most redundacy if you ask me... It think it's a great idea. You can survive a failure of all but 1 disk and still maintain a backup of a max of 1 week old.

in a RAID 5 array you only have to lose 2 disks for the entire set of data to be hosed.