Forum OpenACS Q&A: Re: OT: Dell PowerEdge RAID 10 Configuration
I recently setup one of our Dell 2550 servers with RAID 10 -- I'm using 4 of the 15k rpm 73-GB drives in the array with one hot spare. The disk performance is far better than the RAID 5 this machine was running, which is important for this customer since they have a large number of files (images mostly) being accessed in the filesystem outside of the database.
The fiber-channel attached Apple Xserve Xraid is a good solution, one I'm going to be looking into myself.
Dell distinguishes between RAID 10 and RAID-1 Concatenated:
The RAID Advisory Board considers RAID 10 to be an implementation of RAID level 1. RAID 10 combines mirrored drives (RAID 1) with data striping (RAID 0). With RAID 10, data is striped across multiple drives. The set of striped drives is then mirrored onto another set of drives. RAID 10 can be considered a mirror of stripes. NOTE: This RAID level is used only with PERC 2, PERC 2/Si, PERC 3/Si, and PERC 3/Di controllers.
- Groups n disks as one large virtual disk with a capacity of (n/2) disks.
- Mirror images of the data are striped across sets of disk drives. This level provides redundancy through mirroring.
- When a disk fails, the virtual disk is still functional. The data will be read from the surviving mirrored disk.
- Improved read performance and write performance.
- Redundancy for protection of data.
RAID-10 on PERC 2/SC, 2/DC, 3/SC, 3/DCL, 3/DC, 3/QC, 4/Di, and CERC ATA100/4ch controllers is implemented as RAID Level 1-Concatenated. RAID-1 Concatenated is a RAID-1 array that spans across more than a single pair of array disks. This combines the advantages of concatenation with the redundancy of RAID-1. No striping is involved in this RAID type. Also, RAID-1 Concatenated can be implemented on hardware that supports only RAID-1 by creating multiple RAID-1 virtual disks, upgrading the virtual disks to dynamic disks, and then using spanning to concatenate all of the RAID-1 virtual disks into one large dynamic volume. In a concatenation (spanned volume), when an array disk in a concatenated or spanned volume fails, the entire volume becomes unavailable.
So it appears that RAID 1 concatenated differs from RAID 10 in that there is no striping and if one disk fails in a volume, the entire volume becomes unavailable.
James, Dell's RAID 10 info sounds confused to me. Actually, it reads as if it was written by a secretary after taking notes on something she didn't actually understand.
From the above it is not really clear just what the hell their "RAID Level 1-Concatenated" is, but they presumably mean that it is atually RAID 10 done in 1,0 fashion, which would be good.
But their info above is all confused, they are mixing together discussion of hardware and software RAID without ever explicitly saying so, the whole sentence about "In a concatenation ... the entire volume becomes unavailable." is misleading and only partially accurate, etc.
Also, Matt Domsch, a Dell lead software engineer, confirmed that hot the PERC4-DC will support a global hot spare using specific software from LSI, but you have to manually configure this to do so. Since hot spares are per-controller, not per channel, it's fine to have a hot spare on the 3 side in a 2+3 split channel configuration. If you lose a disk on the 2-side, it'll rebuild onto the spare such that you'll really be running with one channel with one disk plus a bad disk, and the second channel with three disks.
Clearly you did the right thing by tracking down the real info from the manufacturer.
Just a note on Dell...
Dell's definition of raid 10 is NOT the industries standard, the jerks at Dell find it better to keep customers totally confused; confused mushrooms are good for business.
Dell's definition of raid 10 is raid 0+1, which NO one should use, as you can only loose one drive, the second is total array loss. The newer Percs are LSIlogic, and are quit capable of doing industry defined raid 10 (mirrored and striped) or raid 0+1 (stripes mirrored). Anyone confused should go to lsilogic.com and follow their raid 10 setup..
I have a Dell 2600 W Perc4/Di. I called LSI and they said that all they do is supply chips for these cards and Dell does ALL the software for them. He said that if you use LSI software on these cards, you can destroy them. He said contact Dell only for any issues with these cards.
So, Dell says that this controller does RAID 1 - concatenated. I DO NOT believe this is a true raid 10!!!!
RAID 1 concateneted does not stripe, it just fills multiple drives in 1 array, 1 at a time, and then mirrors them.
What the heck it this????
Can a CONCATENATION professional comment here?