this document include SCSI disk and SCSI device parameters, add
cache_type firstly, other parameters will be added later.

Signed-off-by: Weiping Zhang <zhangweip...@didichuxing.com>
---
 Documentation/scsi/sd-parameters.txt | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 Documentation/scsi/sd-parameters.txt

diff --git a/Documentation/scsi/sd-parameters.txt 
b/Documentation/scsi/sd-parameters.txt
new file mode 100644
index 0000000..88ea9a2
--- /dev/null
+++ b/Documentation/scsi/sd-parameters.txt
@@ -0,0 +1,23 @@
+Linux SCSI sd Parameters
+============================================================
+
+scsi disk
+----------------------------------------
+Path: /sys/block/sdx/device/scsi_disk/x:x:x:x/*
+
+* Name: cache_type
+* Description: enable/disable write&read cache
+
+Encoding                   | WCE RCD | Write_cache Read_cache
+-------------------------------------------------------------
+write through              | 0   0   | off         on
+none                       | 0   1   | off         off
+write back                 | 1   0   | on          on
+write back, no read (daft) | 1   1   | on          off
+
+For "temporary", it only change request_queue's flag, not send
+any command to disk, so actually disk'cache doesn't changed yet.
+
+* Usage:
+echo "write back" > cache_type
+echo "temporary write back" > cache_type
-- 
2.9.4

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