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Not only NFS

Not only NFS

Posted Dec 26, 2008 21:16 UTC (Fri) by zdzichu (subscriber, #17118)
Parent article: Justifying FS-Cache

The beatiful example of this second level caching is available in other opearting system for over a year. Imagine caching content from local HDD in insanely fast (hundreds of MB/s) Intel SSD. Using FS-cache, all linux filesystem could gain feature known as L2ARC in ZFS.
(the second interesting ZFS feature, separate intent log, we already have in the form of external journal device in ext3/4).


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Not only NFS

Posted Dec 28, 2008 17:47 UTC (Sun) by oak (guest, #2786) [Link]

> Imagine caching content from local HDD in insanely fast (hundreds of
MB/s) Intel SSD.

Although Flash is fast to read, it's slow to write. What if user's mostly
streaming some huge media files she listens or views once (a month or
year)?

Not only NFS

Posted Dec 29, 2008 2:16 UTC (Mon) by giraffedata (subscriber, #1954) [Link]

Although Flash is fast to read, it's slow to write. What if user's mostly streaming some huge media files she listens or views once (a month or year)?

She doesn't use FS-Cache.

That the FS-Cache configuration doesn't help this user doesn't mean it doesn't help anyone.

Not only NFS

Posted Dec 29, 2008 13:51 UTC (Mon) by dag- (subscriber, #30207) [Link]

Well, it's not really that slow even when it is slower than reading. Here are the stats for my Intel 80GB SSD (on a RHEL5 2.6.18 kernel) with 2 threads:

Sequential writes: 57MB/sec
Sequential reads: 170MB/sec
Random reads: 199MB/sec
Mixed workload (70%R, 30%W): 69MB/sec
Random writes: 72MB/sec

And with 16 treads:

Sequential writes: 48MB/sec
Sequential reads: 208MB/sec
Random reads: 174MB/sec
Mixed workload (70%R, 30%W): 144MB/sec
Random writes: 40MB/sec

Granted, with 16 threads the results are less flattering. But for a single disk, it is not slow compared to other laptop disks.

Not only NFS

Posted Dec 30, 2008 23:00 UTC (Tue) by zdzichu (subscriber, #17118) [Link]

SSD slow at write? Single X25-E can write at 170 MB/s, and Micron RealSSD tops at 250MB/s. Show me traditional disk capable of this. And it's general purpose SSD! I don't know how fast could be write-optimized flash used in hybrid storage NASes, like Sun Storage 7000 line.

There are some awesome benchmark numbers coming from system running ZFS with (~) external log and second level cache. They are coming mostly from extreme number IOPS delivered by flash, but interesting anyway. Just search for L2ARC and slog (separate intent log) results.

Not only NFS

Posted Jan 31, 2009 14:12 UTC (Sat) by zdzichu (subscriber, #17118) [Link]

For the record, this shows how external caching on fast SSD helps performance: http://blogs.sun.com/brendan/entry/l2arc_screenshots
Be aware that warming up cache take hours.


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