RAID5 question

[VJ]

Hello,

Today, my RAID5 controller and harddisks should arrive, and I just thought of something.

Is it better to opt for a single logical drive, or is it better to create multiple logical drives?
(the system will consist of 3 400 GB harddisks, thus yielding 800 GB of storage)

Or doesn't this choice impact performance?

If one adds a drive later on, and chooses to enlarge the raid (in my case to 1200 GB), can one choose which logical drive is enlarged?


Jörg

[Dr Mordrid]

I set mine up as a single logical drive for video. Never considered enlarging since it's been ~1TB since day one, but control over expansion probably depends on the controller/drivers.

[Paddy]

I use a single logical drive

[Gurm]

I don't think it has much of an impact on performance but multiple logical drives makes managing it sort of a pain. Some arrays are limited in the number of drives you can have or the size of a single logical drive. HP's SATA array that I have been working with lately has a logical drive size limit of 2TB, so if you put in more drives than that, then you end up HAVING to make a second Logical Drive.

[Dilitante1]

the one thing to note is once you pick the size for the array, you cannot expand it without rebuilding it from scratch.....

[VJ]

Acutally, the controller (Promise 4300) allows for expanding the RAID if you add an additional drive. It looks to work without loosing the data that is present on the drive.

Thanks, I guess I'll make it a single logical drive (will be 800 GB) just for ease.


Jörg

[KeiFront]

It all depends on the controller/drivers.

[VJ]

Formatting 800GB takes extremely long (it is now 6 hours doing that, and now close to finishing).

This makes me wonder: aren't multiple partitions safer regarding a corrupt file system, etc.?
Or doesn't this matter much for NTFS?

Jorg

[Dr Mordrid]

NTFS is much more robust in such matters, plus if a drive craps or has an error the array contents can be rebuilt once you replace it using the parity drives data.

[MultimediaMan]

I partition my RAID5 arrays: a ~20GB Boot Partition and a data partition for the balance. If other drive letters are needed, I'll setup mount points to directories within the data drive.

This keeps things simple while still adhering to best practices for servers and workstations.

[VJ]

Installing was fun!

My boot disk is on the internal SCSI adapter. When I installed my SATA raid controller, the POST screen of the internal SCSI controller disappeard an the drives were not found to boot from. Removing the SATA controller solved it.

As I had no internet, I just called the SuperMicro technical support line.

They immediatly understood the problem; the solution is in bios settings. Each PCI slot has the options "Option ROM", "Enable Master" and "PCI Latency". The first option determines whether or not the bios for bootable cards is loaded (for which there is limited space). By default, this is enabled for all PCI slots. The internal SCSI bios is the last one to be loaded (if there is ample room).
Disabling the Option ROM for the Promise solved the problem (but of course if I now want to access the Promise bios, I first have to go the the PC bios and enable it). Apparently, the Promise bios takes up more space than the one of an Adaptec 2940UW (as this one was enabled and still allowed for the internal SCIS host to load its bios); disabling the one for the 2940UW still doesn't yield sufficant room to load the Promise one together with the internal SCSI one.
The technical support also checked to see if there was a newer bios that provides for more room to load bioses, but this was not the case.

Either way, their response was fabulous.


Jörg

[Gurm]

I partition my RAID5 arrays: a ~20GB Boot Partition and a data partition for the balance. If other drive letters are needed, I'll setup mount points to directories within the data drive.

This keeps things simple while still adhering to best practices for servers and workstations.

I'm sorry! I thought he was talking about a purely storage array, not a boot array. Wait, he was!

But, in the case of a boot array, then yes a small(ish) boot partition with a larger data partition are called for by best practices. However, I now feel that the "12GB" and "20GB" numbers are wholly inadequate. The average server now runs enough bloated junkware that I'm formatting with 25GB as a starting point, or even 36GB if the customer indicates that they'll be installing a lot of apps. Remember that many poorly-written apps will NOT store their databases anywhere other than the program files directory.

[Gurm]

Formatting 800GB takes extremely long (it is now 6 hours doing that, and now close to finishing).

Yes, it does. Well, it depends. HP's SmartArray controllers actually format the RAID almost INSTANTLY. Or so they claim. The controller just queues up the format and does it while you're not looking. You can install the OS immediately.

DELL arrays, on the other hand, take LITERALLY 12 hours or more to format. *ick*

[VJ]

I first tried a quick format, but for some odd reason I couldn't copy files to it yet. So I then aborted it, went to the bios, redefined the logical drive and started a long format (in the end it took 8 hours).

Oh, just a heads up: if you buy Seagate Barracude ES, there is this jumper that is factory installed and limits the operation to 1.5 Gb/s. It is installed for compatibility with older systems, but can be removed if your system supports 3 Gb/s.
I'm surprised by how silent this array is. I would have expected those 3 harddisk to contribute to the noise, but luckily this isn't the case (but ok, the system was noisy to begin with).


Jörg

[Gurm]

Virtually all modern system noise is fan-based.