Re: [Veritas-bu] Fragment size for LTO4 on NBU 6.x

I'm still on LTO2 and have the max fragment size set to 8GB. That's a file every few minutes if the drive is allowed to run full speed. Will probably multiply by 2 or 4 when I ever upgrade.

Jim VandeVegt
VandeVegt @t yahoo.com

From: oersted <netbackup-forum AT backupcentral DOT com>

tape drive will use LOCATE BLOCK to first file to restore, then search from there.

wdlb5359 wrote:
> What are people using for the fragment size on LTO4 (or I guess LTO3) with
> NBU 6.x?
>
> I ask because the default is 1TB, i.e. more or less don't fragment.
>
> The argument for a large fragment is that the backup doesn't have to stop
> so often as it does briefly at the end of each fragment to update the
> Master, and also the inter-fragment file markers waste space..though
> that's hardly a consideration on such large tapes now.
>
> The argument for a small fragment was that the tape can position at full
> speed to the file marker for the appropriate fragment for a restore,
> rather than reading the tar file from the top at read speed, which for a
> large tape could be a very long time.
>
> We used to (dating back to DLT7000) set a 2GB fragment, as back then this
> was thought a good idea in case you wanted to dd the tape to disk and read
> it without NetBackup. UNIX file systems did not take files > 2GB. Well I
> can't say we ever tried it and it's a silly small size now.
>
> But what are people using - 100GB? 200GB? Does it really make a
> difference...
>
> William D L Brown

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