Re: Typical RAID5 transfer speeds

[Roger Heflin <rogerheflin@gmail.com>]

Michael Evans wrote:
> On Sat, Dec 19, 2009 at 1:35 PM, Roger Heflin <rogerheflin@gmail.com> wrote:
>> Matt Tehonica wrote:
>>> I have a 4 disk RAID5 using a 2048K chunk size and using XFS filesystem.
>>>  Typical file size is about 2GB-5GB. I usually get around 50MB/sec transfer
>>> speed when writting files to the array. Is this typcial or is it below
>>> normal?  A friend has a 20 disk RAID6 using the same filesystem and chunk
>>> size and gets around 150MB/sec. Any input on this??
>>>
>>> Thanks,
>>> Matt
>> Speed depends on how the disks are connected to the system, and how many
>> disks there are per connection, and what kind of disks they are.
>>
>> If your friend had a 20 disk raid6 on one 4port sata pci-32bit/33mhz card
>> with port multipliers his total throughput would be <110mb/second reads or
>> writes, if your friend had 20 disks on 10+ port pcie-x16 cards his total
>> possible speed would be much much higher, reads would be expected to be
>> 18x(rawdiskrate) if the machine could handle it.
>>
>> Also newer disks are faster than older disks.
>>
>> 1.5tb disks read/write at 125-130+ MB/second on a fast port.
>> 1.5tb disks read/write at 75-80 MB/second on a PCI-32bit/33mhz port.
>> 500gb disks read/write at 75-80 MB/second on a PCI-32bit/33mhz port.
>> 250gb disks read/write at 50-55 MB/second on a fast port.
>>
>> And those PCI-32bit/33mhz ports are with only a single disk, put more than
>> one on there, and the io rates drop...so 2 disk on pci-32bit/33mhz (old PCI)
>> port will have <50MB/second each no matter how fast the disk is, put 3 on
>> there and each disk is down to 33mhz, 4 25MB/second or less.
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> 
> Speaking of 16x 16 port cards, why is it that it's so difficult to
> find an 8 or 16 port 4 or 8/16x pcie adapter?  A good 1xpci-e to 2x
> SATA costs like 25 to 50 USD.  Given the reduction in duplicate
> components, it should not be hard to make a card with 8 ports for 100
> USD or less right?  I don't even want any intelligence, just normal
> disk to PCI-E lane connectin would be fine.
> 

I am pretty sure it is lack of need.

I believe someone mentioned supermicro has a 8 port pcie-x4 card, that 
is in the $100 range, but the driver for it is kind of new and has 
some issues at this time.