Re: write-intent bitmaps
Russell Coker wrote: Are there plans for supporting a NVRAM write-back cache with Linux software RAID? AFAIK even today you can place the bitmap in an external file residing on a file system which in turn can reside on the nvram... Peter - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: write-intent bitmaps
On Tuesday 29 January 2008 20:13, Peter Rabbitson [EMAIL PROTECTED] wrote: Russell Coker wrote: Are there plans for supporting a NVRAM write-back cache with Linux software RAID? AFAIK even today you can place the bitmap in an external file residing on a file system which in turn can reside on the nvram... True, and you can also put the journal of a filesystem on a NVRAM device. But that doesn't give the stripe aggregating benefits for RAID-5 or the general write-back cache benefits for everything else. -- [EMAIL PROTECTED] http://etbe.coker.com.au/ My Blog http://www.coker.com.au/sponsorship.html Sponsoring Free Software development - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: write-intent bitmaps
On Tuesday 29 January 2008 05:15, Bill Davidsen [EMAIL PROTECTED] wrote: You may have missed the much higher part of the previous paragraph. And given the reliability of modern drives, unless you have a LOT of them you may be looking at years of degraded performance to save a few hours of slow performance after a power fail or similar. In other words, it's not as black and white as it seems. What is the pathological case? 1/2 or 1/3 write performance? For serious write performance of a RAID you want a NVRAM write-back cache for RAID-5 stripes, and the NVRAM cache removes the need for write-intent bitmaps. AFAIK Linux software RAID doesn't support such things and that putting filesystem journals and the write-intent bitmap blocks on NVRAM devices is the best that you could achieve. It seems that if you want the best performance for small synchronous writes (EG a mail server - which may be the most pessimal application for write-intent bitmaps) then hardware RAID is the only option. Are there plans for supporting a NVRAM write-back cache with Linux software RAID? -- [EMAIL PROTECTED] http://etbe.coker.com.au/ My Blog http://www.coker.com.au/sponsorship.html Sponsoring Free Software development - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
write-intent bitmaps
http://lists.debian.org/debian-devel/2008/01/msg00921.html Are they regarded as a stable feature? If so I'd like to see distributions supporting them by default. I've started a discussion in Debian on this topic, see the above URL for details. -- [EMAIL PROTECTED] http://etbe.coker.com.au/ My Blog http://www.coker.com.au/sponsorship.html Sponsoring Free Software development - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: write-intent bitmaps
On Sunday January 27, [EMAIL PROTECTED] wrote: http://lists.debian.org/debian-devel/2008/01/msg00921.html Are they regarded as a stable feature? If so I'd like to see distributions supporting them by default. I've started a discussion in Debian on this topic, see the above URL for details. Yes, it is regarded as stable. However it can be expected to reduce write throughput. A reduction of several percent would not be surprising, and depending in workload it could probably be much higher. It is quite easy to add or remove a bitmap on an active array, so making it a default would probably be fine providing it was easy for an admin to find out about it and remove the bitmap is they wanted the extra performance. NeilBrown - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: write-intent bitmaps
On Sunday 27 January 2008 22:21, Neil Brown [EMAIL PROTECTED] wrote: On Sunday January 27, [EMAIL PROTECTED] wrote: http://lists.debian.org/debian-devel/2008/01/msg00921.html Are they regarded as a stable feature? If so I'd like to see distributions supporting them by default. I've started a discussion in Debian on this topic, see the above URL for details. Yes, it is regarded as stable. Thanks for that information. However it can be expected to reduce write throughput. A reduction of several percent would not be surprising, and depending in workload it could probably be much higher. It seems to me that losing a few percent of performance all the time is better than a dramatic performance loss for an hour or two when things go wrong. It is quite easy to add or remove a bitmap on an active array, so making it a default would probably be fine providing it was easy for an admin to find out about it and remove the bitmap is they wanted the extra performance. I hadn't realised that. So having this in the installer is not as important as I previously thought. -- [EMAIL PROTECTED] http://etbe.coker.com.au/ My Blog http://www.coker.com.au/sponsorship.html Sponsoring Free Software development - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
