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" <[email protected]> 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
