scsi-config - query information from a scsi device with a nice user interface
queries information from an scsi target with a nice Tcl/Tk
user interface. If you do not specify a device to query, scsi-config
calculates a list of available devices and prompts it to you.
By the nature of a graphical user interface, most things will explain them self.
shows a list of buttons for certain mode pages
which you may press. Those buttons which you can press and the text windows
with white backgrounds can be modified by you and the modifications send back
to the device.
In the main window there is a button to instruct the device to save the data in
some non volatile memory (if it supports it). Note that this will instruct the
device to save the Read-Write Error Recovery Page ,
Disconnect-Reconnect Page , Format Device Page , Caching
Page , and Control Mode Page in its NVRAM. Usually saving even a
single of those should write
them all to the NVRAM, but you never know.
You can query the current, the factory default and the values in the NVRAM
(which may not be the current parameters) from the device.
Not all combinations of button toggles or all values are valid. In general, try
to set them and see which values the drive accepts. scsi-config
the device configuration immediately, s.t. you see which values where
Also note that some disk drives are notched, and that those have an active notch
(shown in the main window) to which all your settings apply (at least those of
notched pages, which are also marked in slate gray). You can select the active
notch to which your settings apply (and to which the values refer) in the
For those devices which do not feature an NVRAM (generally removable media
devices) and as a kind of backup, you can save the current settings to a file.
Actually the file will be a /bin/sh
script making the necessary
(8) calls to set the saved parameters when executed.
There is also a nice Overview button which will query many details about the
disk geometry and draw them in a nice picture. This looks esp. nice for drives
with many notches, that is different regions on the disk with different tracks
per sector settings. It is also very useful for notched drives as you can
immediately select the mode pages for each notch.
- 1. General Warning
- Generally, do not modify settings you don't understand. It
is useful to know the SCSI-II specs mentioned below. Some setting may
render the device unusable or even damage it. Usually a power cycle resets
the state (if you do not save the weird settings in the NVRAM). Some
settings affecting the assignment of logical sectors will render the disk
unusable until the next low level format.
- 2. On Write Caching
- As an old warning, this does also mean you should not
generally switch the write cache on. At least on those drives where you
have a choice at all. Reasons are twofold:
- It is a priori unclear when the drive will actually perform
the writes. This is a bad thing when considering shutdown of your machine.
On the other hand, it seems sensible to assume that the drive will
immediately write it's cache to disk when it is idle (after all file
systems are unmounted) and due to the size of the on disk cache this will
usually only need a few seconds after the shutdown (but the drive lamp
will usually not glow, as it is mostly connected to the host adapter (if
you have a lamp at all) and it is not participating).
There is a SCSI command to flush the caches. Linux could call it prior to
shutting down, spinning a disk down. Due to my knowledge this is not yet
- As the writes are performed asynchronously, errors are
reported asynchronously. The disk might return an error at some simple
read instruction related to a write which was acknowledged OK several
transactions ago. This generally confuses things and makes interpreting
errors very difficult. Some devices are known/said to not report write
errors in this mode of operation at all.
Just imagine that at the point where a file system is unmounted, or a new
removable media is detected it could tell: Oops, BTW, there was some write
error ago although I told you it was OK already.
- Thus, when you run a disk in write cache mode, keep it in
mind when weird error messages occur and give the disk time to flush it's
buffers at shutdown. Generally it would be good if you knew more vendor
specific details on how the disk operates in the write cache mode.
- 3. Reassigning Bad Blocks Automatically
- One of the nice features of SCSI disk is that they allow to
remap bad blocks automatically as they are detected without any user
intervention. However, you actually have to enable this feature! It turned
out that you can not generally assume a disk in this mode. To enable this
mode or check the settings, proceed as follows:
- Go to the Read-Write Error Recovery Page.
AWRE (Automatic Write Reallocation Enable) and ARRE
(Automatic Read Reallocation Enable) buttons enable the automatic
In the same window, you can select the maximal retries performed. EER allows
the disk to do some Early Error Recovery which is fast (but might
misdetect or miscorrect data). A selected DCR button (Disable CoRrection
Codes) disallows the disk to use any error correction codes at all (thus
the drive will have to retry until it performs an error free read).
Usually a sector will be reallocated after even a single read retry or the
given number of failed write retries. When the sector cannot be recovered,
it is reallocated but the data is lost and an error is signalled.
The other buttons there apply to error reporting as well. TB Transmits the
bad Block together with the error, RC Reads Continuous, that is, does not
pause a read operation while retrying or using error code calculations to
recover a bad block (thus may return bad data). PER lets the disk report
even recovered errors (Post ERror), DTE (Disable Transfer on Error) even
breaks a running data transmission when an error is detected.
- Even when the reallocation is enabled, the disk must
actually have some reserved areas where to remap the bad blocks. The
Format Page controls this. Either a given number of Alternate
Sectors Per LUN is set aside for the whole disk or a given number of
tracks is defined to be a zone and for each zone a number of
sectors or tracks is put aside. These alternate data areas are where bad
sectors are remapped.
Note that this page is very likely to apply only to the current notch on a
notched disk device.
If there are no, or not many alternate sectors reserved on your disk, you
must change these settings.
I found that those disks which allow to modify these settings are very often
set to no reserved sectors at all by the vendors, as this increases the
disks capacity. For the sake of stability, you should really modify these
If you decide to modify the number of alternate sectors, you must
- Save the parameters to the NVRAM of the disk.
- Low-level format the disk drive (and not erase the NVRAM
during this operation).
- to make the changes be effective.
- Esp. when you set the disk to not report recovered errors
(or when it is in a write cache mode or something), and just as a general
guideline, keep an eye on the grown defects list where the disk will
report all the remappings which took place as your disk ages.
The old adventurers guide line applies: Save (Backup) Early, Save (Backup)
Often. Find the right time to replace your disk avoiding too much work
recovering your data.
could be enhanced by making better use of Tcl/Tk. I learned
much about it during my work on tk_scsiformat
(8) and their would be
much room for fixes and enhances. On other hand, it fulfils it's purpose as it
is quite nicely already.
makes heavy use of scsiinfo
(8) all it's bugs (esp.
on defect reading) apply.
(Tcl/Tk subroutines used by scsi-config).
American National Standard
for information systems
SMALL COMPUTER SYSTEM INTERFACE - 2
MARCH 9, 1990
Michael Weller <firstname.lastname@example.org>, Versions 1.5 &