The default for the number of the logical volume manager mirror write consistency cache (MWCC) is 62, or 0x3e is the hexadecimal . This number is double the original default and improves the user's write performance, but it also increases the time needed to make all mirrors consistent again at volume-group vary-on time after a crash. These variables are all system load-dependent.
Note: This procedure modifies the LVM device driver binary code using the adb command. Care should be taken when following this procedure.
dump -h hd_pinIn the .data section header is the RAWptr file, which contains a hex address. Record this address to be used later. An example hex address is 0x0000fc00 .
dump -n hd_pin | grep mwcc_entriesThe second field displayed is the offset for the variable. An example is 0x000003f8 .
0x0000fc00 + 0x000003f8 = 0x0000fff8
cp hd_pin hd_pin.orig
abd -w hd_pin
Note: The adb command issues a warning that the string table is missing or the object is being stripped.
0xADDR/Xwhere ADDR is the address you generated in step 4.
If the hd_pin file has not been modified in this way, the adb command responds with:
ADDR: 3eIf this procedure has been done, the adb command responds with:
ADDR: zzwhere zz is the current value, from 0x1 to 0x3e, for the number of MWCC entries. If the value is not between 0x1 and 0x3e, check that you are using the correct address.
0xADDR/W zzwhere ADDR is the address derived in step 4 and zz is a hex number between 0x1 and 0x3e.
The system runs with the size of the mirror write consistency cache set to the new value.
Note: The new mwcc_entries value must be from 0x1 to 0x3e, inclusive. Unpredictable results occur if these bounds are violated.
Serial DASD Subsystem Device Driver in AIX Version 4.3 Technical Reference: Kernel and Subsystems Volume 2.
The lvdd special file.
The write subroutine, readx subroutine.
The bread kernel service, bwrite block I/O kernel services.
The adb command.