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disk-to-disk backup advice?

Mic V.
Esteemed Contributor

disk-to-disk backup advice?

Does anyone have advice on disk-to-disk backups? Pros and cons, experience...?

We are considering using Legato Networker with either Netapp NearStore R100 or EMC CLARiiON for backups to disk that are later written to tape -- trying to improve throughput and the backup window. We want to improve the Notes backups (now very long), as well as general NT backups. HP-UX and Solaris backups will also be consolidated into this one setup. Unknown whether Networker will run on NT or HP-UX.

Points for your thoughts...




P.S. This thread has been moved from General o Disk-Based Backup. - Hp Forum Moderator

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Michael Steele_2
Honored Contributor

Re: disk-to-disk backup advice?

Consider all the bottlenecks involved in a backup and how to improve performance. Your Network or SAN connection into the tape drive will be the biggest bottleneck.

What is the native and compressed speed of the drive and how much throughput can the I/O connection handle? For example, is it a 1000BaseT ethernet connection into a DLT 7000 using compression?

(* For a DLT 7000 10 Mbps is its compressed speed, 5 Mbps is its native, uncompressed speed. *)

Find out if Legato supports Multiplexing. Ask this specifically. Multiplexing is 2 or more jobs backing up the same file system data in parallel.

Find out if Legato supports firmware compression and uses this by default. (* should *).

Regarding the spare disk, run a test with a large file that's about 3gb in size and copy it between disks. Time the procedure.

timex dd if=/source/file of=/dest/file bs=2048

Now copy to tape.

timex dd if=/source/file of=/dev/rmt/0m bs=2048

Now restore from tape.

timex dd if=/dev/rmt/0m of=/dest/file bs=2048

In general I think you'll see a four or five time slow down copying to tape and maybe a 10 to 15 times slowdown restoring from tape, but you'll have to test this with the above commands. Also, I'm just throwing out approximate numbers.

Disk to disk should be very fast.
Disk to tape will be 4-5 times slower. (* guessing *)
Restoring from a compressed file will be slower still.

So memory and CPU are all that's left, AND, the data being backed up. If the data fragmented? If yes then fragmented data will be slower to back up then defragemented. data.

Did you know that data written into a file system for the first time is not fragmented?

I point this out to you because maybe you should ask Legato if they 'newfs' the backup disk file system every time.

Think about it.
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Dave Wherry
Esteemed Contributor

Re: disk-to-disk backup advice?

Quantum has a device designed especially for disk to disk backups. It makes this disk array look like a tape library. It is the DX-30

I've never used it. Quantum came in and did a presentation on it a few months ago. Looks interesting.

Check the compatibility matrix on their site.