[Server-devel] jffs2 vs ubifs vs ext4 space-efficiency question
Any ideas why Release 13.2.6 placed on ext4 instead of jffs2 appears to almost double in size? Starting with 13.2.6 on XO-1 on jffs2 per usual, "du -s /* | sort -nr" yields these contents for a stock/vanilla XO-1: 1070992 /usr 239060 /home 117623 /var 18780 /etc 15382 /boot 8735/versions 1032/run 8/tmp ... Naively summing up the above numbers gives a figure of almost 1.5GB, and yet we all know the XO-1 is limited to 1.0GB :-) Is jffs2 somehow compressing the above files by about 2X, which are clearly contained within 769MB as shown in "df -hT" below? Filesystem Type Size Used Avail Use% Mounted on mtd0 jffs2 1.0G 769M 256M 76% / ... Basic tests putting 13.2.6 on an SD card with ext4 show a rough doubling in size with the same files (du's ~1.5GB of files indeed sum to about 1.5GB when listed using df), which I presume indicates ext4 dispenses with compression, unlike the more space-efficient to jffs2 (and presumably ubifs) etc designed for flash/SD devices ? Apologies for my naivete: Would any ext4 partitioning options (or ubifs instead) offer any functionality similar to this apparently huge compression win offered by jffs2? (Given I'm told jffs2 is not appropriate for the larger SD cards I'm experimenting with, even before we get to wear-leveling questions!) ___ Server-devel mailing list Server-devel@lists.laptop.org http://lists.laptop.org/listinfo/server-devel
Re: [Server-devel] [support-gang] jffs2 vs ubifs vs ext4 space-efficiency question
Yes, jffs2 compresses data. That's why it is so slow. That's why SD card is faster than it should be otherwise. No, there's no commonly used compression for ext4. It would be a performance tradeoff; compression takes time and power. On Tue, Dec 22, 2015 at 04:24:48PM -0500, Adam Holt wrote: > Any ideas why Release 13.2.6 placed on ext4 instead of jffs2 appears to almost > double in size? > > Starting with 13.2.6 on XO-1 on jffs2 per usual, "du -s /* | sort -nr" yields > these contents for a stock/vanilla XO-1: > > 1070992 /usr > 239060 /home > 117623 /var > 18780 /etc > 15382 /boot > 8735 /versions > 1032 /run > 8 /tmp > ... > > Naively summing up the above numbers gives a figure of almost 1.5GB, and yet > we > all know the XO-1 is limited to 1.0GB :-) Is jffs2 somehow compressing the > above files by about 2X, which are clearly contained within 769MB as shown in > "df -hT" below? > > Filesystem Type Size Used Avail Use% Mounted on > mtd0 jffs2 1.0G 769M 256M 76% / > ... > > Basic tests putting 13.2.6 on an SD card with ext4 show a rough doubling in > size with the same files (du's ~1.5GB of files indeed sum to about 1.5GB when > listed using df), which I presume indicates ext4 dispenses with compression, > unlike the more space-efficient to jffs2 (and presumably ubifs) etc designed > for flash/SD devices ? > > Apologies for my naivete: Would any ext4 partitioning options (or ubifs > instead) offer any functionality similar to this apparently huge compression > win offered by jffs2? (Given I'm told jffs2 is not appropriate for the larger > SD cards I'm experimenting with, even before we get to wear-leveling > questions!) > ___ > support-gang mailing list > support-g...@lists.laptop.org > http://lists.laptop.org/listinfo/support-gang -- James Cameron http://quozl.netrek.org/ ___ Server-devel mailing list Server-devel@lists.laptop.org http://lists.laptop.org/listinfo/server-devel
Re: [Server-devel] [support-gang] jffs2 vs ubifs vs ext4 space-efficiency question
On Tue, Dec 22, 2015 at 4:28 PM, James Cameron wrote: > Yes, jffs2 compresses data. That's why it is so slow. That's why SD > card is faster than it should be otherwise. +1 on James reply. Also a quick note: AIUI, jffs2 gets much of its storage advantage from better packing of directory structures & metadata. The overall compression savings include these, and look great. The files contents are not _that_ compressible :-) m -- martin.langh...@gmail.com - ask interesting questions - don't get distracted with shiny stuff - working code first ~ http://docs.moodle.org/en/User:Martin_Langhoff ___ Server-devel mailing list Server-devel@lists.laptop.org http://lists.laptop.org/listinfo/server-devel