Date: Mon, 01 Sep 2003 20:31:42 -0700 From: Bakul Shah <bakul@bitblocks.com> To: Terry Lambert <tlambert2@mindspring.com> Cc: freebsd-current@freebsd.org Subject: Re: swapon vs savecore dilemma Message-ID: <200309020331.h823VgAX040906@gate.bitblocks.com> In-Reply-To: Your message of "Mon, 01 Sep 2003 19:51:57 PDT." <3F5405CD.C5534CBF@mindspring.com>
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> > Is fsck really that memory heavy so that it needs swap? > > Yes, if you have a huge FS. > > The problem is that the checking of the CG bitmaps during an fsck > require that you have all the bitmaps in core Hmm.... For a one TB FS with 8KB block size you need 2^(40-13) bits to keep track of blocks. That is 2^24 bytes or 16Mbytes. That doesn't seem so bad (considering that you really should have a lot more RAM if you are playing terrybytes of data). > My suggestion (which has been my suggestion all along) is to add > two date stamped CG bitmap bitmaps somewhere (my favorite place > for this is to steal space at the front of inode 1, which is used > only rarely, since people don't use the whiteout feature, and > which can be made compatible with whiteouts, in any case). This is the old stable storage idea. You need a generation number rather than a date stamp but the idea is the same. Something needs to be done so that time to fsck depends on the outstanding FS traffic at the time of the crash rather than the size of the FS (especially when you are dealing with multi terabytes of data).
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