Slow parity sync...why?

[ashman70]

So I am building an UnRaid server for a friend using some pretty ancient tech, but hey its free to him. I have the following SATA card installed with all but one of the drives connected to it and the parity rebuild is going at 12MB/s

 

Here is the card:05:09.0 SCSI storage controller: Marvell Technology Group Ltd. MV88SX6081 8-port SATA II PCI-X Controller (rev 09)

 

The board is an old EVGA triple SLI board with a Core 2 Duo on it and 4GB of RAM. I realize these are SATA II speeds, and the drives are a mix of old WD 2TB Greens, 1.5TB greens, some old 750GB and 500GB drives.

[ashman70]

Moved the parity drive to the onboard SATA port, seems to be going at around 19MB/s now which is marginally better, hopefully it will speed up. Just checked and its dropped to 18.8MB/s  sigh.........

[Squid]

Moved the parity drive to the onboard SATA port, seems to be going at around 19MB/s now which is marginally better, hopefully it will speed up. Just checked and its dropped to 18.8MB/s  sigh.........

Move as many of the drives to the onboard as possible.  PCI-X while better than PCI still has some limiting factors.  And your 500GB drive is going to be holding things back as well

 

[ashman70]

Its not even PCI-X its a PCI controller card. OK thanks.

[Squid]

Its not even PCI-X its a PCI controller card. OK thanks.

Then there's your answer.  PCI = Slow as f...

[JorgeB]

Here is the card:05:09.0 SCSI storage controller: Marvell Technology Group Ltd. MV88SX6081 8-port SATA II PCI-X Controller (rev 09)

 

That looks like a PCI-X AOC-SAT2-MV8, but you're using it on a PCI slot, if you can get a cheap board with a PCI-X slot that controller actually as a decent performance, capable 100MB/s+ with 8 disks.

[RickInHouston]

I'm running a parity and its at 69MB /sec. It's been at 95 most of the time, though.

[garycase]

Moved the parity drive to the onboard SATA port, seems to be going at around 19MB/s now which is marginally better, hopefully it will speed up. Just checked and its dropped to 18.8MB/s  sigh.........

 

You're mixing two problems here:  (1)  Since the card is plugged in to a PCI slot, it's limited to 133MB/s ... which you're sharing among about 6 drives (i.e. a max of 22MB/drive -- so if you're getting 19MB you're actually doing well);  and (2) some older drives with fairly low areal density (although I suspect the bandwidth restrictions of the card are still the limiting factor).

 

Use all of the onboard ports before using the card, to reduce the # of drives on that card, and you'll likely improve the performance notably -- but it's still not going to be "good" with that card in a PCI slot.

 

 

[ashman70]

Thanks, I plugged all the drives I could into the six onboard SATA ports then bought a four port PCIe SATA card, array sync'd at between 50-77MB/s after that, much more acceptable.

[garycase]

Thanks, I plugged all the drives I could into the six onboard SATA ports then bought a four port PCIe SATA card, array sync'd at between 50-77MB/s after that, much more acceptable.

 

Yes, that sounds about right for the mix of drives you have.

[garycase]

FYI, you can go here:  http://rml527.blogspot.com/

 

... and look up your specific drives to see which ones have the lowest areal density.  Your old 500GB drives could have platters as small as 167GB;  the 750GB are likely 250GB; etc.    These clearly will provide MUCH slower data transfer than modern drives with 1TB (or larger) platters.

 

[ashman70]

Thanks for the info, I removed all but one 750GB drive and replaced all but two of the 1.5 TB drives with 2TB drives, one of the 1.5TB drives developed one unrecoverable sector last night so I am about to swap it out with a 2TB drive now.

[garycase]

As I assume you know, the slowest drive currently "involved" in a parity check limits the speed -- so even ONE low-density drive will keep the speed slow until that check no longer involves that drive [i.e. if it's a 750GB drive, then once the check passes the 750GB point that drive no longer has any bearing on the speed]