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  1. #1
    Join Date
    Nov 2005
    Posts
    5

    Unanswered: Reducing LDF files

    Hi,
    If I understand it correctly, you only need an LDF file to restore to a point in time after the last full backup? If this is so, then Could the LDF file not be reduced in size on perfoming a full backup?
    Most of the time it's not an issue as there is enough space on the HDD, but is it possible to reduce the ldf file size periodically (manually would be fine). Is changing the recovery mode from FULL to SIMPLE and then back to FULL an option?
    If so, is anyone able to tell me how, exactly, I can do this? ... I've sifted through the documentaion to no avail ...
    Many thanks
    Rob

  2. #2
    Join Date
    Mar 2007
    Location
    Holmestrand, Norway
    Posts
    332
    No, you cannot just truncate the log when you take the full backup, because you do not know whether the error forcing you to restore the database will occur prior to or after the last full backup. You may leave the office at 4pm, at 5 pm some tables disappear. Backups are scheduled to run at midnight. If the logs are truncated when you arrive at the office the next morning, you cannot restore to point in time anymore.

    Thus, the ONLY way you should free space in the logfiles is backing them up with the backup log statement, which frees up place internally in the log files.
    Ole Kristian Velstadbråten Bangås - Virinco - MSSQL.no - Facebook - Twitter

  3. #3
    Join Date
    Feb 2003
    Location
    India
    Posts
    216
    do not change recovery mode FULL to SIMPLE. it will break log chain.

  4. #4
    Join Date
    Dec 2002
    Posts
    1,245

    Thumbs up

    If you are just starting off with SQL Server administration, I would recommend using the maintenance plan wizard (if you are using SQL 2005, be sure to download and install SP2, which has significant improvements to maintenance plans in general).

    General guidelines:

    SQL 7.0/2000:
    1. Create a maintenance plan that includes only the system databases (master, model, msdb). Do a full backup daily.

    2. Create another maintenance plan that includes only the user databases. Do a full backup daily and a transaction log backup as often as you are comfortable (and as often as needed to keep the logs at a stable/reasonable size).

    3. For both plans:
    a. Back up over the network (if your network is stable), or straight to disk (separate from data/log files).
    b. Retain full backups on disk for 2-3 days (more if you can afford it).
    c. Retain log backups for as long as necessary to get back to your last good full backup.
    c. Make sure there's another process that writes the db backups to tape.

    SQL 2005
    1. Create one plan for full backups for all databases

    2. Create another plan for log backups for all user databases.

    3. Follow other guidelines as above.


    There are lots of tweaks and other things that you can do to improve backup performance, this is just a guide to get you started.

    Be sure to also:
    1. Practice recovery:
    a. Practice full database restore
    b. Practive database restore to point in time
    c. Practice recovery from tape
    d. Practice recovery from a dead server (ie, full rebuild/fresh install)

    2. Validate your tape backups

    3. Document your backup strategy and document your recovery plan.


    Regards,

    hmscott
    Have you hugged your backup today?

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