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Mixed speed disks on MSA1000

 
Paul_637
Regular Advisor

Mixed speed disks on MSA1000

I know that the 4314 storage arrays say that you can mix disk speeds (Ultra2/3 etc.) and each disk will still perform at it's rated transfer speeds rather than the "traditional" SCSI issue of all drives slowing to the lowest bus speed on the channel, but haven't seen similar clarification for the MSA1000.

Is it safe to expect the same? Or, would I lower the overall performance of the storage device by putting "slower" bus drives in there (Ultra2's/3's - but in their own Array(s) probably).

Regards,

Paul
11 REPLIES 11
Nguyen Anh Tien
Honored Contributor

Re: Mixed speed disks on MSA1000

Mixed speed and mixed size will reduce the read/write performance.
I recommend that you config all same disk or same speed to once array. do not spread to others disk
HTH
tienna
HP is simple
Paul_637
Regular Advisor

Re: Mixed speed disks on MSA1000

I'm already aware that mixing devices within a single configured array would impede performance. I'm just trying to work out if having "slower" drives in other drive slots within the storage unit automatically slows down the whole SCSI bus to that speed.

In other words, with a 36Gb Ultra3 drive in each of bays 1 & 8 configured as Array A, and two 36Gb Ultra2 disks in bays 2 & 9 configured as Array B, does the Bus speed of the disks in Array B affect the bus speed of the disks in Array A?

If I configure all four disks in a single Array, then I know it would slow them all down.

Paul
raadek
Honored Contributor

Re: Mixed speed disks on MSA1000

Comments about not mixing different types / speeds within RAID array are absolutely valid.

But another concern is about whether to mix or not HDDs with different interfaces (e.g. U160 & U320) on the same SCSI bus. You could have many RAID arrays sharing the same bus, which will perform with the speed of the slowest drive connected to that bus.

First of all the MSA1000 has U160 backpanel interface, which means it makes no difference at all whether you have U160 or U320 speed from your entire MSA30 enclosure - it will be downgraded to U160 anyway.

If you have any drives slower than U160 (e.g. Ultra2) then the best thing to do is to keep them in a separate MSA30.

Regards,
Radek
Don't panic! [THGTTG]
Paul_637
Regular Advisor

Re: Mixed speed disks on MSA1000

Interface speeds is all I'm concerned with at this point, drive (RPM) speeds obviously have an impact if mixed.

Is this definite though? If the 4314 is documented as supporting all devices at their standard interface speed, then it's surprising that a "flagship" device within a similar range doesn't have the same facility?

I'm just trying to make sure that "the best thing to do" isn't just based on traditional SCSI architecture when the newer architecture doesn't have such limitations.

Paul
raadek
Honored Contributor

Re: Mixed speed disks on MSA1000

Yes, the 4314 supports 'all devices at their standard interface speed' - but it still means the entire bus will slow down to the slowest interface of any HDD connected to the bus. I.e. if you mix Ultra2, Ultra3 & U320 it will operate at Ultra2 speed.

The above also applies to the MSA1000 / MSA30.

Basically parallel SCSI interface remained unchanged for years - what we have seen were rather speed bumps that any key architectural breakthroughs.
Don't panic! [THGTTG]
Paul_637
Regular Advisor

Re: Mixed speed disks on MSA1000

Ah, that much isn't made clear in the HP documentation. How misleading! What's the point in supporting all speeds if it can't deliver to them to the host!

Oh well, useful to know...

Actually, how about keeping different speeds on different "halves" of the storage unit? Doesn't it have two buses internally?

So, Ultra3 in bays 1-7, Ultra2 in 8-14 etc. would that make a difference?

Paul
raadek
Honored Contributor

Re: Mixed speed disks on MSA1000

I would guess that having Dual Bus version of the MSA30 could do the job (taken from QuickSpec):
"The dual bus I/O module allows two SCSI channels to access a single MSA30. This allows for greater fault tolerance (controller duplexing) or provides access from two different servers to two separate storage areas."

But for me it is still not rock solid whether the two halves of MSA30 are on separate SCSI buses & can operate with different speeds, or not.

Can anyone confirm that?
Don't panic! [THGTTG]
Uwe Zessin
Honored Contributor

Re: Mixed speed disks on MSA1000

NO NO NO NO NO.

It is not always true that 'all drives will run at the slowest "bus speed"'.

The devices are free to individually negotiate different speeds and use them - that's true for most if not all devices inherited from Compa's / DEC's storage groups.

I have been told that (at least) some initiators from pre-merger HP storage choose to run at the speed of the slowest device, but, again: that is not true of all devices from different vendors.
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Paul_637
Regular Advisor

Re: Mixed speed disks on MSA1000

I have to say that I /thought/ this was the case, but I'd LOVE to see something "official" just for my own sanity.

Can you (or anyone else) suggest any useful reading from HP?

(Appreciate the input!)

Paul
raadek
Honored Contributor

Re: Mixed speed disks on MSA1000

Sorry, but I still do have some doubts. I was taught that SCSI bus due to its parallel architecture will negotiate speed with ALL devices present on the bus & adjust to the SLOWEST device. This is apparently to allow all devices (including 'slow' ones) communicate via the same bus concurrently.

Following has been taken from the MSA30 User Guide:
"The disk system supports up to 14 hot-pluggable, Ultra320 SCSI disk drives. You can also use Ultra3 and Ultra2 drives in the system, but the bus speeds then decrease to the corresponding level."
Don't panic! [THGTTG]
Uwe Zessin
Honored Contributor

Re: Mixed speed disks on MSA1000

I'd like to note that there is conflicting information:
http://h18004.www1.hp.com/products/servers/proliantstorage/sharedstorage/sacluster/msa30/index.html

""Only HP allows for all Ultra320 devices to be compatible with previous Ultra3 and Ultra2 devices so customers can mix and match components in the same storage enclosure or server. When Ultra2 devices, Ultra3 devices and Ultra320 devices are found on the same Ultra320 SCSI bus, each Ultra2 device will transfer data up to 80 MB/s, while each Ultra3 device will transfer data up to 160 MB/s, and each Ultra320 device will transfer data up to 320 MB/s..""

And that is what I have learned in to StorageWorks trainings.

Of course, no disk can be faster than the controller it is attached to. A U320 disk will negotiate down to U160 on an U160 controller.
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