September 30, 200817 yr Hi all, Where can be narrow throat if I copy ISO files to UnRaid server through GLAN from firewire external disk connected to local PC? Thanks for answer
October 4, 200817 yr Hi all, Where can be narrow throat if I copy ISO files to UnRaid server through GLAN from firewire external disk connected to local PC? Thanks for answer Definitely unRAID server itself. Its write performance is way lower than either gigabit LAN or firewire interface limits.
October 4, 200817 yr It *can* be many places... - the external disk - the port the external disk uses to attach to the pc - the lan cabling (cat5+ of better?) - the GLAN switch - the NICs (PC and unRAID) - the unraid data drive - the unraid parity drive Isolate each one and test.
October 10, 200817 yr Is 19,36 MB/sec slow?? I have only around 12-15MB/sec writing speed. Than what's that?
October 12, 200817 yr Author Is 19,36 MB/sec slow?? I have only around 12-15MB/sec writing speed. Than what's that? Yes, I thinkg that on GLAN ~19 MB/sec is slow. This HDD connected in Win workstation have ~78 MB/sec not in RAID.
October 17, 200817 yr Can someone explain me what makes upload speeds to unraid so slow? Is it too weak cpu which cannot calculate parity so fast, or maybe the sata controller?
October 17, 200817 yr Author Can someone explain me what makes upload speeds to unraid so slow? Is it too weak cpu which cannot calculate parity so fast, or maybe the sata controller? Yes, problem my be in SATA controller. SATA cables, HDD, chipset, etc... Which is Your configuration of UnRaid HW?
October 17, 200817 yr Can someone explain me what makes upload speeds to unraid so slow? Is it too weak cpu which cannot calculate parity so fast, or maybe the sata controller? The problem is drive speed.... NOT parity calcs. Even a crappy Pentium II can do parity calcs much faster than the disk can handle them When you write a file to unraid, each sector of data written to unRAID causes: 1) the sector of the data disk to be read 2) the sector on parity to be read 3) a parity calc done on the sector data 4) the new parity sector written 5) the new data sector written. Now reading a sector and immediately writing back new data to the SAME sector on a hard drive is slow, because of drive geometry.... essentially although the data is ready to be written, the drive has to wait for that part of the disk to spin back around under the drive head. This particular aspect can be a significant factor. There are some strategies in controllers and drives that can mitigate this problem, such as NCQ and elevator seeks... anything that lets the drive/controller reorder commands so several sequential reads can take place and once, then several sequential writes. But many of these depend on buffering and simply get swamped when the writes are more than 100x buffer size. Simply increasing buffer size won't help, as the CPU on the drive and on the controller will then be overtaxed by the extra buffer management. So every write you do to unRAID, results in 2 reads and 2 writes..... THAT's one big reason why it is slow.
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