On 7 February 2013 12:54, Amit Kale <ak...@stec-inc.com> wrote: >> -----Original Message----- >> From: Kent Overstreet [mailto:koverstr...@google.com] >> Sent: Wednesday, February 06, 2013 4:01 PM >> To: Amit Kale >> Cc: Michel Lespinasse; Darrick J. Wong; linux-bcache; device-mapper >> development; Kent Overstreet; Mike Snitzer; LKML; Jason Warr; >> thorn...@redhat.com >> Subject: Re: [RFC] [DONOTAPPLY] [PATCH] enhanceio: STEC EnhanceIO SSD >> caching software for Linux kernel >> >> On Thu, Feb 07, 2013 at 06:57:40AM +0800, Amit Kale wrote: >> > > -----Original Message----- >> > > From: Michel Lespinasse [mailto:wal...@google.com] >> > > Sent: Friday, February 01, 2013 4:58 PM >> > > To: Darrick J. Wong >> > > Cc: Amit Kale; linux-bcache; device-mapper development; Kent >> > > Overstreet; Mike Snitzer; LKML; Jason Warr; thorn...@redhat.com >> > > Subject: Re: [RFC] [DONOTAPPLY] [PATCH] enhanceio: STEC EnhanceIO >> > > SSD caching software for Linux kernel >> > > >> > > On Fri, Feb 1, 2013 at 4:44 PM, Darrick J. Wong >> > > <darrick.w...@oracle.com> wrote: >> > > > This is a patch to migrate STEC's enhanceio driver out of their >> > > github >> > > > repository and into the staging tree. From their README: >> > > > >> > > > "EnhanceIO driver is based on EnhanceIO SSD caching software >> > > > product developed by STEC Inc. EnhanceIO was derived from >> > > > Facebook's open source Flashcache project. EnhanceIO uses SSDs as >> > > > cache devices for traditional rotating hard disk drives (referred >> > > > to as source volumes >> > > throughout this document). >> > > > EnhanceIO can work with any block device, be it an entire >> physical >> > > > disk, an individual disk partition, a RAIDed DAS device, a SAN >> > > > volume, a device mapper volume or a software RAID (md) device." >> > > >> > > What's your take on the benefits of this vs bcache ? >> > >> > EnhanceIO was designed for and has been validated in enterprise >> > environments. The important benefits are - 1. There is no downtime >> for cache creation, deletion, editing properties, >> writeback/readonly/writethrough mode change. >> >> True of bcache. >> >> > 2. Wb mode comes with an option to control whether dirty data should >> be clean-up across reboots, which prevents SSD/HDD going out of sync. >> >> No idea why you'd want this. You have to be able to handle a rebooting >> with a dirty cache, if you hope to handle unclean shutdown - bcache >> does this. And if you're running in writeback mode there's probably >> going to be many gigabytes of dirty data in your cache, at least >> sometimes, and you aren't going to want to wait for that to flush >> before you reboot. >> >> If you want to flush dirty data with bcache, you can switch back to >> writethrough mode whenever you want. > > We have two modes of operation with writeback > > 1. Warm restart mode (default) - Reboots are quick. Dirty data is kept as it > is across reboots. So is clean data. Abrupt reboots are handled correctly by > throwing away clean data and retaining dirty data. The throwing away clean > data is a fallout of an optimization done to skip metadata updates for clean > data. > > 2. Cold restart mode - A reboot or a shutdown involves clean-up of dirty > data. This is for paranoid sysads who are afraid that iSCSI HDD setup may > cause them to be reattached. Switching to writethrough mode will achieve the > same thing, however with a persistent cache configuration in place, the cache > will be write-through after a reboot.
How does Enhance-IO prevent mounting of the backing device if the cache device doesn't show up due to failure etc? I was reviewing the setup/tear-down code but I couldn't find where EIO writes any superblock etc to the backing device to prevent udev etc from mounting the filesystem. > > I am happy to see bcache being compliant with the rest of the items I had > noted. > > -Amit > >> >> > 3. Our in-house testing was done for large setups with 500GB+SSDs and >> proportionately large HDDs, on 24CPU machines with plenty of RAM. It's >> survived heavy IO loads without any locking or corruption problems. >> >> True of bcache. >> >> > 4. Error handling is exactly what enterprises look for - >> writethrough/readonly modes work seamlessly regardless of SSD failures. >> In all the three caching modes, the guarantees of completion in >> presence of IO errors or shutdowns, in terms of granularity and >> persistence of data written, is identical to underlying HDDs. >> >> True of bcache. >> >> > 5. It works for all known block devices - Software RAIDs, full block >> devices with or without partitions, individual partitions, various >> intelligent block devices. >> >> True of bcache. >> >> > -Amit >> > >> > PROPRIETARY-CONFIDENTIAL INFORMATION INCLUDED >> > >> > This electronic transmission, and any documents attached hereto, may >> contain confidential, proprietary and/or legally privileged >> information. The information is intended only for use by the recipient >> named above. If you received this electronic message in error, please >> notify the sender and delete the electronic message. Any disclosure, >> copying, distribution, or use of the contents of information received >> in error is strictly prohibited, and violators will be pursued legally. >> >> Which of the above information was proprietary, and should I not be >> resending this to lkml or - who? >> >> ... > > PROPRIETARY-CONFIDENTIAL INFORMATION INCLUDED > > This electronic transmission, and any documents attached hereto, may contain > confidential, proprietary and/or legally privileged information. The > information is intended only for use by the recipient named above. If you > received this electronic message in error, please notify the sender and > delete the electronic message. Any disclosure, copying, distribution, or use > of the contents of information received in error is strictly prohibited, and > violators will be pursued legally. > -- > To unsubscribe from this list: send the line "unsubscribe linux-bcache" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- CTO | Orion Virtualisation Solutions | www.orionvm.com.au Phone: 1300 56 99 52 | Mobile: 0428 754 846 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
