Well, we've done a few more tests. I think the problem is the raid5 system.
When we restore the same Image on the same system on a single drive (instead
on the raid 5 system) the restore is a lot faster :

Raid 5 System :
backup : transfer rate 22 MB/sec
restore : transfer rate 8 MB /sec

restore the same image on the same system on a single drive without raid :
restore : transfer rate between 15-17 MB /sec

Boris


-----Ursprungliche Nachricht-----
Von: Tab Trepagnier [mailto:Tab.Trepagnier AT LAITRAM DOT COM]
Gesendet: Freitag, 13. Januar 2006 19:41
An: ADSM-L AT VM.MARIST DOT EDU
Betreff: Re: [ADSM-L] Backup / Restore IMAGE


Boris,

This is my GUESS.

When reading the disk you take advantage of OS read-ahead caching so the
"backup" performance is limited by the output device or its communication
link.  My LTO-1 drives will each swallow 20 MB/s or better depending upon
compressibility.

When "restoring" to the disk, especially something as large as an image
file, you quickly exhaust the write cache that the OS allocates to the
target disk.  Our experience is once that happens you're lucky to get more
than 5 MB/s per disk.  This is especially bad with ATA disks.  We've seen
them start at 50 MB/s and then after a couple hundred MBs, drop to as low
as 2 MB/s because the write-cache was full.

This applies to SAN/arrays as well.  Our RAID-3 LUN on our SAN could
swallow over 50 MB/s with the write-cache turned on, but when we turned
the cache off - details in an earlier message from me - the performance
dropped to about 12 MB/s.  And our SAN vendor EMC says RAID-3 is optimum
for applications like TSM disk pools.

Tab Trepagnier
TSM Administrator
Laitram, L.L.C.




"ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU> wrote on 01/12/2006
02:58:28 AM:

> Hi,
>
> we've a windows 2003 fileserver with millions of files. On a Testsystem
> (Windows 2003, 3 GB memory, 1 GB Ethernet) we've tried backup image /
> restore image for one drive (69 GB). The Backup was done after 56
Minutes
> (transfer rate 22 MB/sec) . The restore time for this Image was 2:32
hours
> (transfer rate 8 MB/sec).
>
> So our question : Is it normal, that the restore for the image needs 2,5
x
> longer than the backup time?
>
> Thanks for help and kind regards,
>
> Boris