I installed Ubuntu 12.10 and a bunch necessary packages, then downloaded, extracted, configured, and ran make and make install on hamsterdb 2.1.0. Then I downloaded and extracted lessfs 1.5.13. When I run “./configure –with-hamsterdb” configure runs for a while and then halts with this error:

configure: error: “Hamsterdb is not found”

Any idea what could be wrong? Thanks!!

The command to TRIM a hardware SSD exists in two variants, one for ATA/SATA (requires all other I/O to stop during the TRIM) and another one for SCSI (doesn’t, thus potentially more efficient).

To the higher levels in the operating system (NT in your case), iSCSI is no different from any other SCSI connection, and the DISK I/O commands sent to iSCSI are the same commands from the same code (disk.sys on NT) as for any hardware SCSI connection.

Thus if NT supports SSD’s with TRIM on a high end enterprise class SCSI bus (such as SAS or FC), then it should also be able to send a TRIM to an iSCSI target, provided that the iSCSI target tells NT that it actually has a TRIM command and wants it to be used.

The second part of the problem is then to make the SCST code provide TRIM as a feature of its virtual SCSI disks and pass such TRIM commands onto the lower layers (MD, LVM, loop, real disks, lessfs) and for lessfs to recognize and implement it.

To me the biggest hole in this picture is the lack of a standard, flexible, POSIX-style API for doing a TRIM-like operation on any byte range in an arbitrary seekable file (such as a sparse file on ext2 or a real world SSD). Windows has such an API, at least for NTFS sparse files.

thanks for the reply. This is one thing I have also thought about.. simply overwriting the not used blocks with the same data so the deduplication rate would be very high. However this is not the best solution (as from what I understand these zero’d out blocks will still be referenced in the DB, so it would not be “empty space” but “space deduplicated at a very high rate”).
It would be really nice to have a procedure like TRIM for SSDs, but I do not think anything like this exists

first off, thanks for this tutorial. However I am not quite sure how to solve the following problem:
If I present an iSCSI Lun to a host and format it with, lets say NTFS there, when files inside the NTFS file system are deleted the now unused blocks cannot be reclaimed by lessfs because it has not information about these blocks being obsolete now.
Any idea how to work around that?