giacomoleopardo Posted November 22, 2020 Share #1 Posted November 22, 2020 (edited) Hello everybody. Maybe I'm missing something, here, but I can't figure this out. My system: - DSM version DSM 6.2.3-25426 - Loader version and model: JUN'S LOADER v1.04b - DS918+ - Using custom extra.lzma: IG-88's extra and extra2 - Installation type: BAREMETAL - ASRock Fatal1ty Z170 Gaming-ITX/ac, Intel Pentium G4400 SkyLake, 2x4 GB DDR4 RAM, Raid 5 for testing with: - SSD Intel 120 GB - SSD Crucial 120 GB - HDD Toshiba 300 GB - HDD Hitachi 240 GB - Cache: - READ and WRITE 2x 1 TB SATA SSD Crucial Here's the deal. Since Synology declares here: https://blog.synology.com/xmas-wishlist-optimizing-your-nas-with-ssd-cache "Apart from SSD endurance, you should also consider the memory requirements of SSD caching. As an SSD cache requires a certain amount of system memory depending on the cache size, you may have to upgrade your memory if you want to mount a larger SSD cache. To maintain system stability, only 1/4 of the pre-installed system memory is allocated for SSD caching. Since a 1GB SSD takes up approximately 416KB system memory (including expandable memory), a 2 X 128GB SSD read-only cache (total 256GB) requires at least 104MB memory, while a 2 X 128GB SSD read-write cache (total 128GB) consumes 52MB memory. It should be noted that a lack of memory will, therefore, limit the SSD cache size." I can't figure out why when I create my cache raid 1 with the two 1TB SSDs it allows me to gain 321 GB instead of 900/1000 GB. 1000 GB cache would require 416 MB of my RAM, which is far less than 2 GB (a quarter of my 8 GB). Here's a screenshot. Thanks in advance for any help. G. Edited November 22, 2020 by giacomoleopardo Quote Link to comment Share on other sites More sharing options...
giacomoleopardo Posted November 22, 2020 Author Share #2 Posted November 22, 2020 A little update: I tried with my pc RAM (32 GB DDR4 2x 16GB) installed, but the result is the same. I guess that's not a RAM issue Quote Link to comment Share on other sites More sharing options...
bearcat Posted November 22, 2020 Share #3 Posted November 22, 2020 54 minutes ago, giacomoleopardo said: it allows me to gain 321 GB This is when you press the "Max" button? Are you able to write a different size in the box? Quote Link to comment Share on other sites More sharing options...
IG-88 Posted November 22, 2020 Share #4 Posted November 22, 2020 (edited) 2 hours ago, giacomoleopardo said: I can't figure out why when I create my cache raid 1 with the two 1TB SSDs it allows me to gain 321 GB instead of 900/1000 GB. 1000 GB cache would require 416 MB of my RAM, which is far less than 2 GB (a quarter of my 8 GB). go into the dsm resource monitor and check the memory section, there should be information about memory consumption Edited November 22, 2020 by IG-88 Quote Link to comment Share on other sites More sharing options...
giacomoleopardo Posted November 22, 2020 Author Share #5 Posted November 22, 2020 1 hour ago, bearcat said: This is when you press the "Max" button? Are you able to write a different size in the box? Yes, but not more than 321 GB Quote Link to comment Share on other sites More sharing options...
giacomoleopardo Posted November 22, 2020 Author Share #6 Posted November 22, 2020 1 hour ago, IG-88 said: go onto the dsm resource monitor and check the memory section, there should be information about memory consumption Quote Link to comment Share on other sites More sharing options...
IG-88 Posted November 22, 2020 Share #7 Posted November 22, 2020 the RAM looks ok 5 minutes ago, giacomoleopardo said: Yes, but not more than 321 GB maybe that relates to your RAID5 array, its a 4 x 120GB, after the overhead it might be the size of 3 x 120GB (one less because of redundancy) as its only for testing you could make the 4 disks a jbod array and see how the cache suggestion turns out (should be way more if i'm rigt) Quote Link to comment Share on other sites More sharing options...
giacomoleopardo Posted November 22, 2020 Author Share #8 Posted November 22, 2020 Just now, IG-88 said: the RAM looks ok maybe that relates to your RAID5 array, its a 4 x 120GB, after the overhead it might be the size of 3 x 120GB (one less because of redundancy) as its only for testing you could make the 4 disks a jbod array and see how the cache suggestion turns out (should be way more if i'm rigt) Good idea! Thanks for the advice. I'll try asap and report back here. Quote Link to comment Share on other sites More sharing options...
giacomoleopardo Posted November 22, 2020 Author Share #9 Posted November 22, 2020 28 minutes ago, IG-88 said: the RAM looks ok maybe that relates to your RAID5 array, its a 4 x 120GB, after the overhead it might be the size of 3 x 120GB (one less because of redundancy) as its only for testing you could make the 4 disks a jbod array and see how the cache suggestion turns out (should be way more if i'm rigt) Yep, I guess you're right. Here are the cache creation wizard's results, upon a 700 GB JBOD 1 Quote Link to comment Share on other sites More sharing options...
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