Hi, not sure whether there is a minimum physical memory requirement to run zfs? i noticed the "free" phyiscal memory dropped quickly while doing "dd" on zfs files: kthr memory page disk faults cpu r b w swap free re mf pi po fr de sr m1 m1 m1 m2 in sy cs us sy id 0 0 0 203840792 7426912 38 223 80 0 0 0 0 44 26 26 0 137 2837 1085 2 1 97 1 0 0 253459616 7019824 1348 297 18 0 0 0 0 2 1 1 0 105 700 199 0 7 93 7 0 0 252638072 6286464 0 45 80 0 0 0 0 39 19 19 0 59 681 105 0 8 92 12 0 0 250790864 4462304 0 43 17 0 0 0 0 27 14 13 0 97 405 145 0 4 96 13 0 0 249930224 3603192 0 70 42 0 0 0 0 21 11 11 0 128 498 244 0 6 94 12 0 0 249213712 2886480 0 45 23 0 0 0 0 18 9 9 0 101 397 190 0 4 96 15 0 0 248300384 1973264 0 50 27 0 0 0 0 17 8 8 0 107 408 180 0 4 96 5 0 0 247627112 1299456 0 35 13 0 0 0 0 3 1 1 0 48 343 84 0 3 97 7 0 0 247056016 726784 0 9 9 0 0 0 0 3 2 2 0 50 739 85 0 6 94 please address me directly since i''m not on the zfs-discuss alias. thanks, cecilia
Hello Cecilia,
Tuesday, November 14, 2006, 3:01:42 AM, you wrote:
CL> Hi,
CL>
CL> not sure whether there is a minimum physical
CL> memory requirement to run zfs?
Generally requirements are similar if you would use different file
system.
CL> i noticed the "free" phyiscal memory dropped
CL> quickly while doing "dd" on zfs files:
It''s because ZFS doesn''t use page cache and it uses kernel
memory.
Side effect is you see almost all free mem drop to 0. When memory is
needed zfs should get back memory but there are circumstances (read
bugs) it doesn''t.
--
Best regards,
Robert mailto:rmilkowski at task.gda.pl
http://milek.blogspot.com
On 11/13/06, Robert Milkowski <rmilkowski at task.gda.pl> wrote:> Generally requirements are similar if you would use different file > system. > > CL> i noticed the "free" phyiscal memory dropped > CL> quickly while doing "dd" on zfs files: > > It''s because ZFS doesn''t use page cache and it uses kernel memory. > Side effect is you see almost all free mem drop to 0. When memory is > needed zfs should get back memory but there are circumstances (read > bugs) it doesn''t.Are there any plans to expose the size of the zfs page cache so that the vmstat "free" column is useful again? Consider an environment where you run a bunch of J2EE apps that are memory bound. In the pre-zfs world, a reasonable way to track "how full" a server is is to use vmstat''s free column. Now, after backups hit the server the first time and brings about physmem worth of data from disk, vmstat''s free hovers close to zero until the next reboot (or zpool export). This (currently) leaves me with the following options to get the info that I have without ZFS: 1) Add up the rss of all the running processes, run pmap on all of them, then figure out how much RAM is really being used. This is troublesome at best and impossible if there are too many short-running processes. Oh, wait... the kernel uses some memory too. 2) Use mdb to look at zfs`arc->size. This may be more attractive if exposed through kstat. Neither of those options is very attractive. Does anyone know of relevant RFE''s that are in the works to improve the situation, or should I file one and stop complaining. :) Mike -- Mike Gerdts http://mgerdts.blogspot.com/
Is this true, that ZFS does not require more memory than any other file system? I am planning to run ZFS on a low memory system (~256MB) and I''m hoping this will be sufficient. This message posted from opensolaris.org