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alexpeshkoff 2007-11-26 08:55:45 +00:00
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doc/README.raw_devices
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@ -1,12 +1,12 @@
Issue: Issue:
====== ======
When database in forced writes mode grows rapidly, file system When database in forced writes mode grows rapidly, filesystem
disk operations produce a serious overhead, making performance disk operations produce a serious overhead, making performance
up to 3 times lower compared with turned off forced writes. up to 3 times lower compared with turned off forced writes.
Scope: Scope:
====== ======
Mainly affects linux, because linux misses appropriate system Mainly affects Linux, because Linux misses appropriate system
call to make database file grow efficiently. call to make database file grow efficiently.
Document author: Document author:
@ -18,38 +18,38 @@ Document date: 2007/11/21
To make firebird have better performance under such circumstances To make firebird have better performance under such circumstances
you may place your database not in a regular file on some you may place your database not in a regular file on some
filesystem, but on raw device. Any type of block devices is filesystem, but on raw device. Any type of block devices is
supported. supported.
For example: For example:
gbak -c my.fbk /dev/sda7 gbak -c my.fbk /dev/sda7
will restore your database on the third logical of extended will restore your database on the third logical of extended
partition of your SCSI(SATA) disk0. partition of your SCSI(SATA) disk0.
Known issue: Known issue:
To be able to do physical (using nbackup utility) copy of To be able to do physical (using nbackup utility) copy of
database you MUST specify explicit name of difference file: database you MUST specify explicit name of difference file:
# isql /dev/sda7 # isql /dev/sda7
SQL> alter database add difference file '/tmp/dev_sda7'; SQL> alter database add difference file '/tmp/dev_sda7';
This is required because default location of difference file This is required because default location of difference file
will be in /dev, which is surely not what you need. It's also will be in /dev, which is surely not what you need. It's also
better to know how many blocks on block device are actually better to know how many blocks on block device are actually
occupied (or you will have to copy all data on raw device, occupied (or you will have to copy all data on raw device,
which can make size of your copy abnormally large). To obtain which can make size of your copy abnormally large). To obtain
real size of database, you should use '-S' switch of nbackup: real size of database, you should use '-S' switch of nbackup:
# nbackup -s -l /dev/sda7 # nbackup -s -l /dev/sda7
77173 77173
Where 77173 is a number of pages, occupied by database. Take Where 77173 is a number of pages, occupied by database. Take
care - this is database's page size, not disk physical block care - this is database's page size, not disk physical block
size! If unsure, use size! If unsure, use
# gstat -h /dev/sda7 # gstat -h /dev/sda7
Database "/dev/sda7" Database "/dev/sda7"
Database header page information: Database header page information:
@ -58,22 +58,22 @@ Database header page information:
Generation 43 Generation 43
Page size 4096 <== that's what you need Page size 4096 <== that's what you need
ODS version 11.1 ODS version 11.1
. . . . . . . . . . . . . .
You may use nbackup output directly in a script, performing You may use nbackup output directly in a script, performing
database backup: database backup:
# DbFile=/dev/sda7 # DbFile=/dev/sda7
# DbSize=`nbackup -L $DbFile -S` || exit 1 # DbSize=`nbackup -L $DbFile -S` || exit 1
# dd if=$DbFile ibs=4k count=$DbSize | # compress and record DVD # dd if=$DbFile ibs=4k count=$DbSize | # compress and record DVD
# nbackup -N $DbFile # nbackup -N $DbFile
Or perform physical backup using nbackup: Or perform physical backup using nbackup:
# nbackup -B 0 /dev/sda7 /tmp/lvl.0 # nbackup -B 0 /dev/sda7 /tmp/lvl.0
In all other aspects raw devices do not have known specific In all other aspects raw devices do not have known specific
acpects of use. in use.
Tip: it's good idea to have raw devices in aliases.conf - in Tip: it's good idea to have raw devices in aliases.conf - in
case of HW reconfiguration of your server you will not need to case of HW reconfiguration of your server you will not need to
change connection strings. change connection strings.