Re: SiI 3112 & Seagate drivers

[Tejun Heo <htejun@gmail.com>]

Kanniball wrote:
> Well let's see if we can get the tecnical info...
> This is a very annoying problem... so please "devs" give us the info we need, 
> and we'll try to do your best

  Hello, Kanniball.

  I've digged lkml previously and what I've found out are

  * It's basically because of faulty SATA implementation of the affected 
seagate hard drives combined with standard-compliant but peculiar 
behavior of silicon image controllers.

  SATA communicates using packets which is called FIS in SATA 
terminology.  When transferring data for read/write, the data can be 
tranferred splitted on multiple packets.  The standard doesn't limit 
where the data can be splitted, but most controllers split them on block 
  (512 byte) boundaries.  Unfortunately, siimage controller doesn't 
always split them on block boundaries and some (well, many) seagate 
drives depend on packets split on block boundary.  So, that's where 
everything goes wrong.

  * Data FIS maximum payload size is 8k, or 16 blocks.  And siimage 
controllers doesn't split packets on odd boundaries (maybe not at all) 
when data size is equal to or less than 15 blocks.  So, sata_sil driver 
sets max_sectors to 15, and the drive never gets to transfer more than 
one page at a time.  So, it's dog slow.

  * As the problem occurs only when writing data, we can improve read 
performance to normal level, but the current block/libata driver 
structure isn't structured to support separate limits on reads/writes 
and the developers don't wanna change it because of some faulty hardware.

  * I don't know how Windows drivers handle this but from the past 
posts, it seems that Windows driver also has the blacklist.  It would be 
nice if someone can verify siimage+seagate read/write performance on 
Windows.  And it would be even better if someone with SATA tracer would 
investigate how the gruesome-twosome act on Windows.

  * The cleanest way would be some form of firmware updates for either 
the siimage controller or seagate drives.  Unfortunately, this doesn't 
seem to be feasible; otherwise, they would have come up with it way back.

  * To top it all, both companies keep details regarding above buggy 
behavior under strict NDA and continue to sell faulty devices.  Way to 
go, Silicon images / Seagate. OTZ

  * It seems that IDE/libata developers contacted both companies in the 
past without any positive result, so I doubt they will act any 
differently this time.  But, my heart, too, is with you.

  Thanks.

-- 
tejun