35babe0ae5
set on some files as a workaround for binary check. - Fix pathname for svn co in the webupdate script. Approved by: doceng (implicit)
284 lines
10 KiB
Text
284 lines
10 KiB
Text
<!DOCTYPE HTML PUBLIC "-//FreeBSD//DTD HTML 4.01 Transitional-Based Extension//EN" [
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<!ENTITY base CDATA "../..">
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<!ENTITY date "$FreeBSD$">
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<!ENTITY title "Large data storage in FreeBSD">
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<!ENTITY % navinclude.developers "INCLUDE">
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<!-- Status levels -->
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<!ENTITY status.na "<font color=green>N/A</font>">
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<!ENTITY status.done "<font color=green>Done</font>">
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<!ENTITY status.wip "<font color=blue>In progress</font>">
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<!ENTITY status.untested "<font color=orange>Needs testing</font>">
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<!ENTITY status.new "<font color=red>Not done</font>">
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<!ENTITY status.unknown "<font color=red>Unknown</font>">
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<!-- The list of contributors was moved to a separate file so that it can
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be used by other documents in the FreeBSD web site. -->
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<!ENTITY % developers PUBLIC "-//FreeBSD//ENTITIES FreeBSD Developers Entities//EN"> %developers;
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]>
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<html>
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&header;
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<h2>Contents</h2>
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<ul>
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<li><a href="#background">Purpose and background</a></li>
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<li><a href="#testing">Testing large capacities</a></li>
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<li><a href="#userland">Userland Tools Status</a></li>
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<li><a href="#ifnet-status">Kernel Driver Status</a></li>
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</ul>
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<a name="background"></a>
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<h2>Purpose and background</h2>
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<h3>The UFS filesystem</h3>
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<p>When the UFS filesystem was introduced to BSD in 1982, its use of 32
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bit offsets and counters to address the storage was considered to be
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ahead of its time. Since most fixed-disk storage devices use 512 byte
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sectors, 32 bits allowed for 2 Terabytes of storage. That was an almost
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un-imaginable quantity for the time. But now that 250 and 400 Gigabyte
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disks are available at consumer prices, it's trivial to build a hardware
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or software based storage array that can exceed 2TB for a few thousand
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dollars.</p>
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<p>The UFS2 filesystem was introduced in 2003 as a replacement to the
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original UFS and provides 64 bit counters and offsets. This allows for
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files and filesystems to grow to 2^73 bytes (2^64 * 512) in size and
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hopefully be sufficient for quite a long time. UFS2 largely solved
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the storage size limits imposed by the filesystem. Unfortunately, many
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tools and storage mechanisms still use or assume 32 bit values, often
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keeping FreeBSD limited to 2TB.</p>
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<p>We need to ensure that FreeBSD supports large storage sizes and that
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the benefits of UFS2 can actually be realized so that FreeBSD can remain
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relevant in the enterprise world. This page describes known issues and
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limits and provides a focus for further auditing, validation, and
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fixing.</p>
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<h3>Limits on disk partitioning</h3>
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<p>The first limit that is encountered is in disk partitioning. For x86
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and amd64 PC's, the FDISK MBR table is used by the BIOS to partition the
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disk into logical extents and identify which partition ('slice' in FreeBSD
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terms) to boot from. The MBR is defined to use 32 bit disk offsets,
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and since it's an industry standard and interoperability is required,
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there is nothing that can be done to change this. As long as booting a
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PC requires the MBR, the boot slice in FreeBSD is going to be limited to
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2TB.</p>
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<p>The GPT partitioning scheme was introduced with the ia64 architecture
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as an MBR replacement. It provides 64 bit offsets and allows for an
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arbitrary number of partitions. It also provides a compatibility mode
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with MBR where it can generate an MBR-compatible structure on the disk
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for use with systems that don't understand GPT. However, to get the
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full benefits for boot storage, the BIOS and the FreeBSD loader must
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understand it. For secondary storage, GPT can be used by any
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architecture regardless of BIOS or boot support.</p>
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<p>Many systems don't require an MBR or GPT, and even PCs don't require it
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if booting and inter-operating with other OS's is not required. The next
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limit that comes in, though, is with the BSD disklabel. This label
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defines up to 8 partitions on a disk, MBR slice, or other storage extent
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for filesystems and swap space. Unfortunately, the on-disk format of the
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disk label again uses 32 bit quantities, so it is also limited to 2TB.
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Fixing this would require creating a new format that is incompatible
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with the old and would require an update to the FreeBSD boot loader.
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This would complicate interoperability and the upgrade path. Also, if a
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new format is going to be created, it should also address the 8 partition
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limit that exists now. Given these requirements, it's tempting to just
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adopt the GPT format instead for secondary storage partitioning.</p>
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<a name="testing"></a>
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<h2>Testing large capacities</h2>
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<p>Even though large drives are cheap, it still isn't always feasible or
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economical to test on real hardware. Swap-backed memory disks, via the
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md(4) driver, can provide a good substitute for some of the testing.
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Backing with swap means that only the pages that are dirtied by data
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are actually allocated, so a multi-terabyte storage can be simulated
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with a minimal amount of physical RAM+swap. Note that this is less true with
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UFS1 since it will initialize all of the inode blocks during newfs,
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which will dirty quite a bit of data. But for UFS2, swap-backed md
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has the potential for working well. Unfortunately, the kernel md driver
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has a number of 32-bit size limits of its own that need to be fixed.
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Details are provided below.</p>
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<p>It is still possible to avoid disklabels and MBRs for testing by
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using newfs directly on the raw disk or md disk. Sysinstall can be
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tested from a running system by just selecting Expert mode and just
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performing the MBR and disklabel steps. Beware that sysinstall might
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have other bugs that will wipe out your existing system, so care must
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be taken here!</p>
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<a name="userland"></a>
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<h2>Userland Tool Status</h2>
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<p>The following userland tools need auditing and testing for 64-bit
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cleanliness:</p>
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<table class="tblbasic">
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<tr>
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<th> Task </th>
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<th> Responsible </th>
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<th> Last updated </th>
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<th> Status </th>
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<th> Details </th>
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</tr>
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<tr>
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<td>newfs</td>
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<td>&a.pjd;</td>
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<td>19 Sept 2004</td>
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<td>&status.done;</td>
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<td>Handling of '-s' option was fixed. Newfs should be now fully usable
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for large file systems.</td>
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</tr>
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<tr>
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<td>df</td>
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<td> </td>
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<td> </td>
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<td>&status.new;</td>
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<td>An audit is needed to make sure that all reported fields are
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64-bit clean. There are reports with certain fields being incorrect
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or negative with NFS volumes, which could either be an NFS or df
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problem.</td>
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</tr>
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<tr>
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<td>du</td>
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<td>&a.pjd;</td>
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<td>7 Jan 2005</td>
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<td>&status.done;</td>
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<td>Big files/directories handling was broken. It was fixed and du
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should be now fully usable on large file systems with large
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files/directories.</td>
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</tr>
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<tr>
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<td>growfs</td>
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<td> </td>
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<td>12 Sept 2004</td>
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<td>&status.wip;</td>
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<td>Growfs has problems with expanding to new cylinder groups. It also
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initializes UFS2 inode blocks instead of leaving them for lazy
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initialization. It also needs a 64-bit audit.</td>
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</tr>
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<tr>
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<td>sysinstall</td>
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<td> </td>
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<td> </td>
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<td>&status.new;</td>
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<td>A full audit is needed. Reports exist of problems with >1TB
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partitions.</td>
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</tr>
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<tr>
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<td>fsck_ffs</td>
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<td>&a.pb;</td>
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<td>15 Jan 2005</td>
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<td>&status.wip;</td>
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<td>A full audit is needed. At least some printf format changes are
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necessary.</td>
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</tr>
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<tr>
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<td>dump/restore</td>
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<td> </td>
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<td> </td>
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<td>&status.new;</td>
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<td>A full audit is needed. At least some printf format changes are
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necessary in dump(8).</td>
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</tr>
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<tr>
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<td>fsdb</td>
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<td> </td>
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<td> </td>
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<td>&status.new;</td>
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<td>A full audit is needed. At least some printf format changes are
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necessary.</td>
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</tr>
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<tr>
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<td>quota tools</td>
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<td>&a.des; & &a.mckusick;</td>
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<td> </td>
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<td>&status.done;</td>
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<td>Extensive changes are need. Disk quotas are currently
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handled as 32-bit quantities, which limits the maximum
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possible quota at 2TB. Two tasks are needed: 1) have the
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current tools (kernel+userland, edquota for example) fail
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gracefully when presented with 64-bit quantities and 2)
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extend the quota file format and tools to 64-bit while
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providing a compatibility mode and/or migration tools.</td>
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</tr>
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</table>
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<a name="Kernel"></a>
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<h2>Kernel Driver Status</h2>
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<p>Many storage peripherals simply are not designed to handle >2TB
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capacities. For those that are, an audit should be done to verify
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that their drivers handle the sizes correctly and pass those sizes
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correctly to the rest of the kernel.</p>
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<table class="tblbasic">
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<tr>
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<th> Task </th>
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<th> Responsible </th>
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<th> Last updated </th>
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<th> Status </th>
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<th> Details </th>
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</tr>
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<tr>
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<td>md</td>
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<td>&a.pjd;</td>
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<td>17 Sept 2004</td>
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<td>&status.done;</td>
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<td>Swap backed disks can now be created up to 16TB in size on i386.
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This corresponds to 2^32*4096.</td>
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</tr>
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</table>
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<h2>Subsystem Status</h2>
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<p>Some filesystem-related subsystems require testing with >2TB volumes, or
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need to be adapted. The following areas have been identified:</p>
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<table class="tblbasic">
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<tr>
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<th> Task </th>
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<th> Responsible </th>
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<th> Last updated </th>
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<th> Status </th>
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<th> Details </th>
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</tr>
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<tr>
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<td>snapshots</td>
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<td>&a.pb;</td>
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<td>15 Jan 2004</td>
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<td>&status.wip;</td>
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<td>Taking snapshots fails on filesystems >2TB, returning EFBIG
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(on a 5TB filesystem) and subsequently crashing the system in
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softupdates.</td>
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</tr>
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<tr>
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<td>quotas</td>
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<td>&a.des; & &a.mckusick;</td>
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<td> </td>
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<td>&status.done;</td>
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<td>The quota subsystem handles 32-bit quantities, which
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limits quotas to 2TB. Blockings of the syncer have been
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observed while attempting to set quotas over that limit
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(try 4000000000 KBytes as a hard limit in edquota(8) for
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some uid, then create somes files owned by that uid). See
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also the userland entry for quota tools.</td>
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</tr>
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</table>
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&footer;
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</body>
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</html>
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