September 23, 2003 at 6:29 am
Hi!
I have a HP Netraid 4M ultra3, with 128Mb Read/Write cache, controller with 2 Raid arrays on it: Raid5 (6x18Gb Data), Raid1 (logs) + 1x18 (Hot Spare disk) The Raid1 for OS is on integrated controller.
At this time the Raid5 array is split on 2 channels (the controller has 4)
Ultra3 protocol allows up to 160Mb transfer on a bus. The data volume on Raid5 never comes close to this number. The normal data transfer is a few Mbs, cause MS SQL reads data in extends of 64Kb.
I believe, that splitting a Raid array into different channels has no use in this case and at best does nothing, at worst harms performance.
Am I right?
September 23, 2003 at 2:40 pm
quote:
Am I right?
Yes. Last time I calculated this, Ultra3 bus speed (160MB/s, not Mb/s) became a factor only with more than 9 busy 15Krpm drives on a channel.
BTW, it's helpful to put the log array on a different controller (not just channel), as that way you can segregate sequential i/o from random i/o and tune the read/write cache memory ratios differently for each purpose.
--Jonathan
--Jonathan
September 24, 2003 at 6:02 am
But if you only have one Controller then a seperate channel is advised.
September 24, 2003 at 6:12 am
quote:
But if you only have one Controller then a seperate channel is advised.
The RAID1 (with logs) is on a separate channel. I was wondering if splitting a RAID5 array (6x18Gb 10k) into 2 channels is good or bad or doesn't matter.
September 24, 2003 at 7:38 am
quote:
I was wondering if splitting a RAID5 array (6x18Gb 10k) into 2 channels is good or bad or doesn't matter.
If you're using hot-plug drives, and I hope you are, then you will need a backplane for each channel. There will be no performance difference with so few drives.
--Jonathan
--Jonathan
September 26, 2003 at 7:10 am
quote:
If you're using hot-plug drives, and I hope you are, then you will need a backplane for each channel. There will be no performance difference with so few drives.
Perhaps I am missing something... What is backplane?
September 26, 2003 at 8:13 am
quote:
Perhaps I am missing something... What is backplane?
That's the connector board that the cable from the controller and the hot plug drives plug into. Inside a server there is usually one backplane per drive cage, and cages can be serially connected into one virtual backplane. If, as you write, your array is currently using two channels, its drives must be divided between two backplanes.
--Jonathan
Edited by - jonathan on 09/26/2003 08:13:13 AM
--Jonathan
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