Changeset 128 for trunk/src/os2ahci/README

Timestamp:

Oct 14, 2011, 10:22:12 PM (14 years ago)

Author:

cjm

Message:

• Added IBMS506$ character device driver to support existing SMART tools

• Finishing touches to SMART support

• Updated READNE with information around "/f" command line parameter and SMART support

File:

• trunk/src/os2ahci/README (modified) (4 diffs)

trunk/src/os2ahci/README

@@ -57 +57 @@
  - ALP Assembler (part of DDK)
  - link.exe (part of DDK)
+
+Please note that builds other than the official binary delivered as
+part of eComStation releases or downloaded from ecomstation.nl are
+not officially supported by Mensys.
 
 
@@ -101 +105 @@
 /t                     Perform thorough PCI ID scan; default = on, can be
                        turned off with /!t to perform only a PCI class scan
+/f                     Force the use of the HW write cache when using NCQ
+                       commands; see "Native Command Queuing" below for
+                       further explanation
 /r                     Reset ports during initialization (default = off
                        unless the [Intel] AHCI controller was found to be
-                       initialized by the BIOS to SATA mode)
+                       initialized by the BIOS in SATA mode)
 /a                     Set adapter for adapter-specific options
                        (default = -1, all adapters)
@@ -173 +180 @@
 option "/n" to OS2AHCI.ADD.
 
+NCQ and HW Caches
+-----------------
+
+In NCQ mode, OS2AHCI supports a request flag which allows upstream code
+(e.g. file systems) to force writes to go directly to the disk instead
+of being buffered in the HW disk cache. However, at least JFS doesn't
+support this flag properly which effectively disables the HW disk cache
+for write operations across the board, resulting in a substantial
+performance loss. In order to prevent OS2AHCI from disabling the HW
+cache when so requested by upstream code, please use the command line
+option "/f".
+
+This may, of course, result in data loss in case of power failures but
+apparently this was the situation with previous IDE drivers as well thus
+shouldn't make much difference in the field. The JFS code also seems to
+imply that this flag has never been widely supported by [IDE] drivers;
+otherwise, the JFS developers should have stumbled over the performance
+loss a long time ago and fixed the code.
+
+NOTES:
+
+ - Without NCQ, OS2AHCI behaves like former IDE drivers, i.e. the HW
+   cache will always be enabled (on modern disks).
+
+ - When suspending, rebooting or shutting down, OS2AHCI always flushes
+   the HW disk cache regardless of the "/f" or "/n" command line options.
+
 
 Interoperability With IDE Drivers
@@ -278 +312 @@
 always done via DMA.
 
+
+SMART Support
+=============
+
+Starting with version 1.22, OS2AHCI supports the IOCTL interface required by
+existing SMART monitoring tools. Since those tools are hard-coded to open
+the character device named "IBMS506$", OS2AHCI will now register a device
+with this name, too.
+
+NOTES:
+
+ - If multiple drivers exporting this character device name are loaded at
+   the same time, the driver loaded last will receive all [SMART] requests.
+   This means that if both DANIS506 and OS2AHCI are loaded and SMART support
+   for OS2AHCI-controlled hard disks is desired, OS2AHCI will have to be
+   loaded after DANIS506. It also means that DANIS506 may have to be told
+   to ignore type 2 controllers (i.e. controllers supporting both SATA and
+   AHCI) using the command line options "/A:x /I".
+ 
+ - The IOCTL interface for SMART is based on the idea of IDE controllers
+   with a master and a slave drive. OS2AHCI maps all devices (ATA or ATAPI)
+   sequentially to this pattern. If, for example, you have 4 hard disks and
+   one CDROM attached to a single controller on ports 1, 2, 5, 7, and 11,
+   SMART tools will see 3 controllers as follows:
+
+    - controller 0, master: HD on port 1
+    - controller 0, slave:  HD on port 2
+    - controller 1, master: HD on port 5
+    - controller 1, slave:  HD on port 7
+    - controller 2, master: CDROM on port 11
+
+ - The DSKSP_GEN_GET_COUNTERS interface is currently unsupported; calls to
+   the corresponding IOCTL will return 0 for all counters. SMART counters
+   are not affected by this limitation, i.e. SMART tools will be able to
+   report counters from the physical disk; this limitation only affects
+   the software counters maintained by ADD drivers which do support the
+   DSKSP_GEN_GET_COUNTERS IOCTL request.
+