15 hdd's or what?!

[Yamanipanuchi]

So i'm a tinkerer, don't have excess money to spend on shiny new hardware but still like to tinker with servers and PC's.

That being said I have been handed a Dell MD1000 disk array with 15 500gb HDD in it. Want to set it up and use it for fun/playing around. ALL data that will reside on this system will have a firm copy someplace else or will be replaceable.

Question is, should I run all 15 HDD's in zraid3? Or some other configuration. Performance isn't an issue (2-3 devices accessing it here and there).

I know there will be other challenges with this overall setup and i'm just taking it on for a learning experience. I'm still just not sure what type of raid I should go with?

 

[cyberjock]

I wouldn't do 15 disks in a single vdev just because you'd never do that with real-world data to begin with, so why learn the ins and outs of a configuration that you'd be silly to do in any real-world environment?

ZFS behaves differently when you go that wide and the last thing you want to do is take that experience and assume you understand ZFS. You won't. ;)

I'd do two 7-disk RAIDZ2s and keep the last as a spare. ;)

 

[Yamanipanuchi]

Awsome! Straight to the point! That was what I was looking for. That is the secondary option I was looking into.

 

[Carlos Capriotti]

Out of curiosity, it is known that each SAS channel can manage up to 4 direct sas/sata devices.Normally Dell PERCs have two channles, making a total of 8 devices directly controlled. In order to manage more that that you have to have either multiple controllers, or a HBA which I think you have on that MD1000.


An HBA will split disk performance, while multiple controllers would handle disks with their full capacity.


Not being familiar with the MD1000, but having my fair share of experience with Dell hardware, I would like to know what you have there, and if you took the time to measure performance on your implementation. I was dying to put my hands on one of those, but was never sure about the performance you can get out it.

Cheers,

Carlos

 

[Yamanipanuchi]

Out of curiosity, it is known that each SAS channel can manage up to 4 direct sas/sata devices.Normally Dell PERCs have two channles, making a total of 8 devices directly controlled. In order to manage more that that you have to have either multiple controllers, or a HBA which I think you have on that MD1000.


An HBA will split disk performance, while multiple controllers would handle disks with their full capacity.


Not being familiar with the MD1000, but having my fair share of experience with Dell hardware, I would like to know what you have there, and if you took the time to measure performance on your implementation. I was dying to put my hands on one of those, but was never sure about the performance you can get out it.

Cheers,

Carlos

I am using an HBA controller(Dell - Model escapes me at the moment), Im only using 1 channel. MD1000 can split the unit using two channels, But because I got the unit for free (Otherwise would have done something else) I didn't want to spend the money on another cable. The old Perc5 controller it came with really was cumbersome to configure to work with a software raid system.

No, I did not do any performance tests with the unit. I'm using it for personal bulk storage and movie streaming. Its more then capable of keeping up with my needs.

 

[Ericloewe]

Out of curiosity, it is known that each SAS channel can manage up to 4 direct sas/sata devices.Normally Dell PERCs have two channles, making a total of 8 devices directly controlled. In order to manage more that that you have to have either multiple controllers, or a HBA which I think you have on that MD1000.


An HBA will split disk performance, while multiple controllers would handle disks with their full capacity.


Not being familiar with the MD1000, but having my fair share of experience with Dell hardware, I would like to know what you have there, and if you took the time to measure performance on your implementation. I was dying to put my hands on one of those, but was never sure about the performance you can get out it.

Cheers,

Carlos

You seem to be very confused:

Most SAS controllers (RAID or HBA) support 8 channels (some do 4 or 16). SAS channels are generally exposed through SFF 8087 connectors (or the newer, SAS3 connector), which carry four individual channels and enclosure management data.

An HBA does no "splitting" whatsoever. An HBA is an SAS controller that directly exposes the drives it controls to the OS with the SCSI or ATA command sets, as opposed to a RAID controller, which exposes a virtual drive.

An SAS expander allows for several SAS devices to be connected to a single channel (generally four or eight channels for some 20-32 devices), sharing the bandwidth.

 

[Carlos Capriotti]

You seem to be very confused:

Most SAS controllers (RAID or HBA) support 8 channels (some do 4 or 16). SAS channels are generally exposed through SFF 8087 connectors (or the newer, SAS3 connector), which carry four individual channels and enclosure management data.

An HBA does no "splitting" whatsoever. An HBA is an SAS controller that directly exposes the drives it controls to the OS with the SCSI or ATA command sets, as opposed to a RAID controller, which exposes a virtual drive.

An SAS expander allows for several SAS devices to be connected to a single channel (generally four or eight channels for some 20-32 devices), sharing the bandwidth.

Eric, thanks for the reply. Actually this is precisely why I posted the comment (rather than an answer). Terminology is confusing. When you look at a controller, you often find the label "CHANNEL A", "CHANNEL B", and so on. Well, that is actually the SAS connector you mentioned, which actually packs four SAS channels. So far, so good.

Now from your comment, I understand that the SAS expander (which I mistook by the HBA, sorry) will expose each device individually, using one single SAS channel, and that is where the speed sharing or splitting comes from. Have I got it right this time ?

 

[Yamanipanuchi]

To add to the explanation above, The MD1000 literally has a switch on the front of the unit that allows you to "Split" the unit into to two separate arrays (One 7 disk array and one 8 disk array). You can choose to either connect each array to separate machines or use two separate channels (Of four) on your HBA effectively giving you more throughput if needed.

I had to refer back to the owners manual as to what the switch does. I had a hard time believing it did this also. The unit is 7 years old, At the time there probably was more demand to have multiple servers connected to it instead of one large array.

 

[Ericloewe]

Eric, thanks for the reply. Actually this is precisely why I posted the comment (rather than an answer). Terminology is confusing. When you look at a controller, you often find the label "CHANNEL A", "CHANNEL B", and so on. Well, that is actually the SAS connector you mentioned, which actually packs four SAS channels. So far, so good.

Now from your comment, I understand that the SAS expander (which I mistook by the HBA, sorry) will expose each device individually, using one single SAS channel, and that is where the speed sharing or splitting comes from. Have I got it right this time ?

An SAS expander takes a certain number of SAS channels (typically a multiple of four due to the nature of SFF 8087) and switches them so that a larger number of devices (drives or other expanders, again in multiples in four, generally) can be connected, sharing the bandwidth. This is transparent to the host system, but there is a maximum limit of devices a single controller can be connected to (probably at least 128 for LSI SAS 2 HBAs).